For anyone wondering why you can't invade pre-FTL planets:

You have to build an observation post and reveal yourself to the pre-FTL civilization. Then you can invade them.

Reason for that is the fact that xenophiles are blocked from the "aggressive"-First-contact option.
So you have to contact them first (reveal yourself) and then invade.

this does not appear to be working

I prefer to be morally ambiguous. this mod helps ᗜˬᗜ

Always found these kinds of mods and the "xenophiles can purge/Egals can do slavery" mods really funny, like people really want to invade primitives, enslave and purge xenos but they still want to be the "heckin good guy egalitarian xenophile democracy" while they do it.

"We are saving you. Please do not resist"

Time to assist those brave revolutionaries!

"You are being uplifted, please do not resist."