Hi, I'm playing on a highly modded game (Angel/Bob/Clown/APM+more) and cannot keep up with the biter expansion. I'm still in early game and mostly busy with destroying biter bases but in the time I destroy one base, they settle around 2-4 new ones. I have tried reducing biter "Action points scaling" but it seems to have no effect. Is there any other setting to just decrease the frequency and total number of actions the biters have? It is like around 1 newly settled base per minute at the moment ...
(Don't get me wrong, I do like the biters to be aggressive, creative and all, but if destroying any biter base in early game just multiplies their number, there is no way I can even build a simple factory - I have only just reached electricity + automation and not even expanded beyond the starting resources.)

AI point scaling affects passive exapansion over time too. But it doesn't affect settlement due to nest destruction.
It works roughly like this: every destroyed base allows Rampant to create a new base. 3/4 of these are created far from the player, but 1/4 are nearby
Additionally, approximately every 20 minutes a resource deposit is captured.
Sometimes, the AI can ​​switch to siege mode. In this mode, approximately one base is created every 5 minutes near the player.
Also, you may have been unlucky and have experienced a couple of sieges in a row

Also, if you happen to turn on the "AI: Survival Mode" map setting, things are very different there.

Everything mentioned above is about Rampant for Factorio 2.1.
In 2.0, the algorithm is completely different.

The problem is that destroying one nest gave the biters around 1000-1500 action points, allowing it to create around 4-5 squads. Out of these, usually 2 formed a settlement. Then there were the regular expansions at the same time, so my actual destruction:settlement ration was about 1:4 even when I left my factory completely unattended to only roam and destroy biters for some expansion room.
It did help a bit to set AI: Difficulty to "light" (it was at the "hard" default before). Let's see if I can at least manage to continue building my factory now.

Could it be that Bob's Enemies and the enemy factions play a role in multiplying expansion?
[Also, I'm playing on Factory 2.1, yes]

At least indirectly. Their nests are added to the existing "vanilla" ones. And Rampant's activity depends on the total number of nests.
However, the nests near the player base have the greatest impact. The more of them, the more frequent the attacks and the more frequent the spread of the enemy across the map

You might want to turn on the action point display (debug mode in mod map settings) to get a better idea of ​​what's going on

"The problem is that destroying one nest gave the biters around 1000-1500 action points, allowing it to create around 4-5 squads": They are spent only on attacks. Settling costs "siege points" and "settler points."

Yeah, that's what I did. Destroying one nest showed an action point gain of around 1000-1500 as I said. Those were then spent on 4-5 squads of which some attacked and others settled. So the biters kept expanding even though I spent all my time "debugging"...

Ok, I tried a while more on difficulty set to "light". Now I am able to contain biter expansion, but kind of spending 2/3 of my playing time on it. And that's at 0,00% evolution still. Playing with increasing evolution would make it simply impossible.
If you're able to introduce a setting for the frequency of biter expansion like there is in vanilla, I'd very much appreciate that. Right now, I'm playing biter wars and not factorio anymore.

Perhaps you should disable siege mode