They die in walls, cause tps rips.

Can you add setting to disable their clouds? Or somehow combine clouds into 1 so it wont cause UPS issues.

You've guessed one of the upcoming improvements.
However, UPS mostly falls not because of the cloud upon death, but because of the cloud when they attack.
The attack will be changed in one of the updates.

If you can also make some improvements to any biters that do AOE damage, they cause barely any damage, but do it to a lot of entities, so the game is not very happy with it.

According to tests, the animation is solely to blame. Even 2,000 "spawner biters" don't cause as much lags as 10 constantly attacking juggernauts. However, after the change, the lags disappears

Damn, so its not damage but animations that cause "DDOS" attacks. Biters couldn't win, so they started attacking my friend's connection by DDoS-ing his pc xD.

Also, if biters try to combine into one unit (the thing when they cross large parts of map combined) they can start lagging the game bad.

I noticed it happen the most when you artillery strike them. They seem to enter sort of a loop of combining and separating when damaged lagging the fuck out of the game.

(Written from phone.)

Incorrect. It's not the "compression to 1" that causes lag, but the "Vanilla" target search when taking damage and there's no suitable target nearby.
This is especially noticeable if you try to set a crowd of Biters on fire with a flamethrower, far from the base.
Or, for example, in the editor, set a tree on fire and place a bunch of biters nearby. There will be severe lag even without mods.

Unfortunately, there's nothing that can be done. Target acquisition every time damage is a built-in mechanic in Factorio. The only way to combat this is to make it unprofitable to fire at Biters with artillery, so players avoid it. Which is what I am gradually doing - the use of artillery is associated with many risks.

Dnno about what's more risky:

Getting hit with a nuke biter and getting wiped from the face of existence VS throwing literal tons of steel and explosives from a safe distance.