Hello i am able to answer the first and maybe the second one of your points. First yes online fix works quite well i managed to make it work on whiskey running wine on a mac and played online with tunneling using playit gg. So i guess on linux it should as well. I played many games using online fix like Palworld and Lethal company and never had issues. Just a note online fix requires u to have steam u for it to work. That is why i opted for tunneling. But it worked well between my friends on windows. The game itself ran on mac on whiskey but couldnt connect via steam we couldn’t figure this part.

For the second one i was able to use BepinEx for Lethal Company mods and worked you just need to tweak things on whiskey to be able to run dll files in my case.

I hope this helps

1. Yes, at least the ones that use steam should work without too much trouble, not sure about the ones that use epic for multiplayer
2. Yes, trainers work with pirated copys, i did have some issues with wemod a few years ago and dont know if anything changed since then but i do know that fling trainers work

TG is down right now, the earlier post mentions it

https://lemmy.dbzer0.com/post/33138900

As for the third one related to tgx you can look at this post https://sh.itjust.works/post/29312472

Tldr: it’s having problems and we don’t know why

I’ve been using Online-Fix on Linux Mint for a decent amount of time, and I haven’t encountered any issues with it. If Proton can run the game, I’m confident it can also run the Online-Fix patches