Lutris is awesome.
Open source games, games with their own launcher, games on steam, gog, etc are all in it. Can pick to run things natively on Linux, use proton (pick your version or just use latest), wine, or choose from others, and it does it seamlessly. For games you already have installed on steam, you don't need to reinstall them, it finds them and makes them runnable from within lutris once you connect your steam account, you can also install games that you own on any of your connected launchers, and browse/download your undownloaded games from them

Examples for some of the stuff I have all in it now:
Catacyslm: DDA catapult launcher (free and open source game - highly recommend you try it out. Takes some getting used to, but there isn't much you can't do. Also, make sure you get cataclysm-tiles or use a launcher. ASCII is pure, but hard to get used to. Also, DO NOT buy it on steam.)
All of my installed steam games
Cyberpunk 2077 and the witcher 3 via gog
FFXIV (the official launcher, not steam)
Vintage story (open source but not free - highly recommend if you like open world survival crafting games with a big emphasis on survival)

I know, I use it. I'd prefer an official Galaxy port though.

I wrote a guide for getting fallout london up and running if you need a hand

https://lemmy.world/post/18456924