If you haven't gotten any/many 5* operatives yet, then you may want to know what the 4* operatives are good at, and how to put together a good team with them, even if you don't have much/any investment put into them.
Lyfe - Wednesday
Good range and damage, and the game gives you a good weapon for her (Work-in-Progress) as part of the Main Story rewards, as well as lots of Manifestation shards.
Note that almost all of Wednesday's damage comes from her SMG, not her drones.
Wednesday is a versatile dps - decent dps, decent range, decent mobility, decent overall.
Fenny - Lionheart
Shorter range than Wednesday, but better mobility, high ATK and damage, and strong Parts Break potential make Fenny a great dps.
Mauxir - Meow
Meow has an SMG with decent range, a very high fire rate, and decent damage overall.
Meow can use her Ultimate Skill to add a huge amount of damage to some of her shots, increasing her damage by a vast amount, albeit with low uptime.
Meow performs slightly worse than Wednesday for most content, but performs better when Meow's Ultimate is active.
When her Ultimate is active, Meow is the strongest 4* operative, but her Ultimate has low uptime.
Cherno - Those Two
Those Two deals quite a lot of damage with her SMG, and her ult can add a good amount of damage, but her ult has low uptime.
Chenxing - Ethereal Cloud
Chenxing deals decent dps with her assault rifle, but her standard skills drop pods also deal good damage as well, although the pods are completely stationary.
Acacia - [Redacted]
Acacia can rapidly throw out daggers that deal significant damage to groups, although her single-target damage isn't nearly as good.
Against single-targets Acacia can shoot her gun and spam her daggers, but her gun deals ballistic damage, and her daggers deal Skill damage.
Dealing two different types of damage means most support skills won't affect both of her damage types, but you can generally just focus on Acacia's skill damage.
Acacia tends to be the best 4* operative against groups, but isn't that great against single-targets.
Nita - Hands
Nita does deal respectable damage and her skills do give her decent AoE capabilities.
Her skills are melee-range and her shotgun has a short range though.
Her shotgun deals ballistic damage, whereas her skills deal Skill damage, Since support effects usually buff one or the other, Nita benefits less from support effects.
Marian - Queen of Pain
With her Neuronic, QoPs support skill gives a -20% Chaos Resistance debuff for 10s, albeit only to unshielded targets.
Combined with weapon and logistics debuffs, QoP is an excellent support for dps operative that deal chaos damage.
Marian isn't very good as a support for operatives that don't deal chaos damage, but for operatives that do deal chaos damage, Marian is their best 4* support.
The two 4* Chaos-damage dps operatives are Acacia - [Redacted] and Cherno - Those Two.
Acacia, Marian, and Chenxing work very well as a three-person team.
Cherno works best with Fritia, and does work very well with Marian, but Marian doesn't boost Fritia's damage.
Fritia - Little Sunshine
Fritia's Support Skill adds damage to each shot (or shotgun pellet) which can add up to a lot of extra damage for operatives who hit a lot like Wednesday and Lionheart.
Since almost all 4* operatives tend to deal primarily ballistic damage with a high Rate-of-Fire, Fritia tends to be the most useful 4* support overall.
Chenxing - Ethereal Cloud
Chenxing's Support Skill can provide a standard skill damage buff once she has the associated Neuronic, and provides skill dmg buffs once she has some Manifestations.
For operatives that deal skill damage, Chenxing is their best support.
Mauxir - Meow
Meow's Ultimate Skill can add Frost damage to each shot (or shotgun pellet).
Meow's Ultimate Skill has a very long cooldown and a very high U-Energy cost, but it can add a huge amount of damage to each shot.
Yao - Quiet Quitter
Yao's Support Skill deploys a drone that provides strong PBAoE healing.
Chenxing - Ethereal Cloud
Chenxing's Support skill deploys a drop pod that throws out some healing.
Chenxing's healing is much lower than Yao's, but she is the second best (i.e. only non-Yao) 4* healer, and she does also provide some damage buffing too.
Haru - The Ace
Haru does offer ok damage at very long-range, and with auto-aim as well, but overall her damage is very low, and the extra range isn't typically that useful.
Haru also offers a mix of ballistic and skill damage that doesn't really work that well with any of the 4* support operatives.
Siris - The Goldfish
Siris can use her dodge plus Standard Skill to buff her next shot, but that's very clunky and doesn't really increase her dps by that much.
Overall Siris has great survivability, but once you have a healer like Yao that becomes much less important, and Siris' lack of dps makes her very bad overall.
Overall, Siris is basically just Fenny but with a bit less damage and mobility.
Enya - Big Sis
Bis Sis is terrible in every way.
DPS: Lyfe - Wednesday / Fenny - Lionheart / Mauxir - Meow / Cherno - Those Two
Support: Fritia - Little Sunshine
Healer: Yao - Quiet Quitter
Fritia adds Thermal damage to each shot with her Support Skill, so Fritia will add a lot of damage to operatives who deal a lot of hits.
Since Fritia adds damage per hit, operatives that can do a lot of hits work best, so SMGs work best, and ARs and shotguns work well (shotguns fire 8 pellets, each of which do proc Fritia's buff).
Wednesday has decent damage, decent range, and her ult gives her good AoE capabilities, and her SMG has a high fire rate, so Fritia can add a lot of hits.
Wednesday can summon drones, which add passive damage, but their shots don't proc Fritia.
Fenny's shotgun deals high damage, has strong Parts Break, and the high number of hits means Little Sunshine's Support Skill buff adds a lot of damage.
Meow has a high fire rate, and her ult adds even more damage, so during her ult she's very strong, but otherwise is a little bit weaker than Wednesday or Lionheart.
Mauxir also has a high-RoF SMG, so Fritia can add a good amount of damage.
Wednesday, Meow,and Those Two don't really need to move, meaning they can stay inside Yao's PBAoE healing very easily.
Whilst Fenny does tend to stay close to enemies, you can just deploy Yao's healing drone after getting up close to heal you as you deal damage.
DPS Acacia - [Redacted]
Support Marian - Queen of Pain
Support Chenxing - The Observer
+ Healer Chenxing can heal to a decent extent.
Acacia deals good damage against groups using her standard skill, which can be quickly and easily spammed.
With her Neuronic, Marian's support skill gives a chaos resistance damage debuff to unshielded targets, increasing Acacia's chaos damage.
With her Neuronic, Chenxing's support skill gives a standard skill damage buff, buffing the damage of Acacia's daggers.
It also gives additional skill damage buffs after Chenxing gets some Manifestation levels.
Chenxing's support skill also heals to a decent degree, allowing her to buff and heal at the same time.
Acacia deals much worse single-target damage than Wednesday and Fenny, but Acacia having two good supports to buff her damage does help with that, as Lyfe and Fenny both only have Fritia and can't really make good use of a second 4* support. Acacia is better at dealing with groups than Wednesday or Lionheart
DPS Cherno - Those Two
Support Marian - Queen of Pain
Support Fritia - Little Sunshine
Cherno deals Chaos-damage, and Marian debuffs the enemies Chaos resistance, increasing Cherno's damage.
Fritia adds Thermal-damage per-shot, which Cherno does a lot of.
Marian doesn't buff the damage that Fritia adds, but this is still an extremely strong 4* team overall.
Whilst this is generally the highest-dps team conprised of only 4* operatives, you're usually better off having a healer, as 4* operatives have quite low dps, and if you are using 4* operatives then you likely don't have much investment into your operatives yet, so a healer is likely more useful to you than some more damage.
All of the 4* operatives are weak when compared to the 5* operatives.
In endgame content, you will stop using the 4* operatives once you start getting 5* operatives, as the 5* operatives just perform vastly better.
If you have 5* operatives, there is no reason to use 4* operatives except for fun.
If you did want to use a 4* operative as a dps in endgame content, then these are the teams I would recommend for that purpose:
Since the 4* operatives don't actualyl deal that much damage, their best support is generally Tess - Phantasia, who adds Frost-damage to each shot (or shotgun pellet), which can add a lot of damage, whilst Tess also buffs your ballistic damage, which is what most 4* dps operatives primarily deal.
Vidya - Celestial Swan is the games strongest support, as her Support Skill massively debuffs the resistance of the damage type the enemy most recently took, meaning in order for her to work, you need the entire team to only deal one damage type.
Marian - Aquila also works well for 4* operatives, as she provides completely generic but very strong damage boosts, whilst also dealing some Kinetic damage of her one.
The other 5* supports just buff the damage of your dps, rather than adding their own damage, but the low damage of the 4* operatives means they are usually not as good as the above three, although some of them can work well.
DPS: Mauxir - Meow [Meow must be using a Frost-damage SMG to work with this team. It doesn't really matter which SMG it is.]
Support: Tess - Phantasia
Support: Vidya - Celestial Swan
Phantasia gives Meow a lot of ATK and Ballistic damage buffs, and Meow's SMG fires at a very high Rate-of-Fire, allowing the per-shot Aptitude buff from Phantasia's Support Skill to add damage to each of Meow's shots, adding a huge amount of damage to Meow.
Since both Meow and Tess only deal Frost damage, they can be supported by Celestial Swan, who is the games strongest support and massively debuffs an enemies resistance to the most-recently received damage type (Frost-damage, in this case), whilst also buffing the squads damage of that type.
Most of this teams damage comes from the extra damage that Phantasia adds to Meow, which is massively buffed by Vidya.
If you wanted to use a 4* operative as a dps, then this team is by-far the strongest - no other team even comes close.
Note that using Mauxir's Standard Skill will cost time that Phantasia won't be adding any damage for, so avoid using Mauxir's Standard Skill for this team.
You can potentially use any non-Wednesday operative in this team, provided they shoot at a high rate and only deal Frost damage, however for all non-Meow 4* dps operatives this means not using any of their skills and using a Frost-damage weapon, which is a dps loss compared to using their ideal weapon and using their skills, so Meow works out much better as she can use all of her skills (as they all deal Frost-damage) and use her ideal SMG (which also deals Frost damage), and her Ultimate is very strong and adds a lot of Frost damage.
This means that whilst you can use any non-Wednesday operative in this team, there isn't any reason to use any operative other than Meow - Meow does work the best.
Again, Meow + Phantasia + Celestial Swan is by-far the best team that uses a 4* operative as a dps, by a large margin.
DPS: Lyfe - Wednesday / Mauxir - Meow / Fenny - Lionheart / Cherno - Those Two / Siris - The Goldfish / Chenxing - The Observer / Fritia - Little Sunshine
Support: Tess - Phantasia
Support: Marian - Aquila
Phantasia adds Frost-damage to each shot (or shotgun pellet) allowing these 4* operatives to proc Tess a lot for a lot of extra damage.
Phantasia also gives good ATK and ballistic damage buffs as well, increasing the damage of the 4*'s shots by a huge amount.
Aquila buffs the damage of the deployed operative, and adds some Kinetic-damage of her own as well.
Phantasia adds so much more damage than what the 4* operative deals that simply having Phantasia on the team with a high-RoF 4* is enough to deal good damage.
The teams below buff the damage of the 4* operative, which isn't as effective as the 5* dealing lots of damage, as 4* dps operatives deal much lower damage than 5* operatives.
DPS: Fenny - Lionheart / Siris - The Goldfish / Haru - The Ace / Nita - Hands
They must be using a Kinetic-damage weapon to work with this team.
Support: Marian - Aquila
Support: Vidya - Celestial Swan
Aquila massively boosts the teams damage, whilst also dealing some Kinetic damage of her own.
Lionheart and The Goldfish both deal ballistic damage, whereas Haru mostly deals skill damage via her Standard Skill, and Nita deals a mix of both, however Aquila boosts all damage types, so what damage type they deal doesn't matter - in order to work with Celestial Swan it just needs to be Kinetic-damage.
Celestial Swan massively boosts the teams [Kinetic] damage.
DPS: Lyfe - Wednesday / Mauxir - Meow / Fenny - Lionheart / Cherno - Those Two / Siris - The Goldfish / Chenxing - The Observer / Fritia - Little Sunshine
Wednesday must be using an Electric-damage SMG to work with this team.
Meow must be using a Frost-damage SMG to work with this team.
Lionheart must either use a Kinetic-damage shotgun, or not use her skills at all.
Cherno must either use a Chaos-damage SMG, or not use her skills at all.
Siris must either use a Kinetic-damage shotgun, or not use her skills at all.
Chenxing must either use an Electric-damage AR, or not use her skills at all.
Fritia must either use a Thermal-damage AR, or not use her skills at all.
Support: Fenny - Starshine
Support: Vidya - Celestial Swan
Starshine' Support Skill gives special clips to the deployed operative, which give a large amount of ATK and Ballistic buffs, massively increasing their damage whilst the clip is active. Starshine works well with any operative who deals mostly ballistic damage.
Celestial Swan buffs the damage type the team most recently dealt, but since Starshine doesn't deal damage, only the damage type of the 4* matters - so the 4* operative needs to deal one type of damage only [hence the weapon/skill damage-type requirements].
DPS: Lyfe - Wednesday / Chenxing - The Observer
They must be using an Electric-damage weapon to work with this team.
Support: Yao - Nightglow
Support: Vidya - Celestial Swan
Wednesday deals decent damage with her SMG, and Chenxing deals decent damage with her AR.
Nightglow gives ATK, Ballistic, and Crit buffs, improving the ballistic damage of the 4* operative.
Since Nightglow constantly deals Electric damage, the 4* needs to deal Electric damage to work with Celestial Swan, who massively increases the teams [Electric] damage.
DPS: Cherno - Those Two [Those Two must be using a Chaos-damage SMG to work with this team]
Support: Mauxir - Shadow Ka
Support: Vidya - Celestial Swan
Those Two deals good damage with her SMG, which Shadow Ka can massively improve via her ballistic buffs.
Shadow Ka constantly deals Chaos damage, so in order for Celestial Swan to work, Those Two must also deal Chaos damage, and thus must use a Chaos-damage SMG.
Celestial Swan massively boosts the teams [Chaos] damage.