Suggestion (Required)

Idk if its just me but I have this problem where there is illager structure almost everywhere. I'm using tectonic for world gen but this is too many illager structures, would be epic if I could change the generation rate.

Structure generation is controlled via data packs. The default values are similar to pillager outposts and villages.
You can change the values yourself if the defaults don't work well for your setup.

How do i go about doing that?

Look here at structure and structure_set and check the wiki for explanations.

https://github.com/Fuzss/illagerinvasion/tree/main/1.20/Forge/src/main/resources/data/illagerinvasion/worldgen