Does anyone know the current state of gaming on Linux?

I'm 100% ready to remove Windows on my main PC but, the main thing that is stopping me is the gaming aspect. I did see like a year or two ago there was some nice things happening (e.g. proton) but, I have games from other places other than steam and AFAIK proton isn't for 100% of games and stuff.

I would set up a Windows VM and run the games through that but, all the tutorials I've seen have like 2 graphics cards (one for Linux and one to pass through to the VM) and my current setup won't allow for that (had the system for 6 years now, maybe it's time for a full upgrade).

This should give you a pretty good idea. For example, Cyberpunk seems to run pretty well which is impressive considering how buggy the game can be even on Windows. Proton has been an excellent experience for me so far... And you can use it for non-steam games. It's just a fork[0] of Wine with DXVK and some other Wine "extensions" baked in.

[0] https://github.com/ValveSoftware/Proton

Also good luck buying a new GPU in the next 4 years :)