Fork is certainly technically the correct word, but "distribution" might give more the right impression.
I built a Linux gaming desktop 5 years ago. The only thing that regularly causes more than minor issues is that many online games use incompatible anticheat technology. I pretty much play exclusively single-player games on PC, so it hasn't been a practical issue for me.
The performance hit is surprisingly low. It's not rare for the windows binary to run better on linux than the native one (when it's an option)
This is not a Unity game, but especially with ancient stuff like Red Alert? I would certainly try it and expect good results. Some years ago, Wine always used to give me trouble and never worked unless you used some special blend of options (like Proton and PlayOnLinux help with). Maybe those times have passed
We used to play Generals at LAN parties all the time - but once multicore CPUs hit the market, it was difficult to just get to the end of a game, because peers would desync and you'd suddenly find yourself playing singleplayer. Its clearly some race condition in the game engine which makes the game non-deterministic in a multicore situation. Does anyone know - is that still a problem?
Modding the game to work properly at a high framerate doesn't sound very hard when you have the original assets & source code to work from.