I run No Man's Sky on Nobara Linux, installed it on my old laptop that barely gets by on Windows. Really breathed new life into it and I haven't had troubles.

Just installed it on steam after checking the box for proton compatibility. You might need to run a task kill command if it gets stuck in a DirectX install loop on launch but other than that it's been smooth sailing for me.

BG 3 runs on the Steam deck, mostly without issues (except for those that aren't Linux related, like text being hard to read due to the small display and lower frame rate due to the portable hardware).

I can say offhand that No Man's Sky put a lot of extra time and effort into their Steam Deck support so that definitely works. Otherwise your best bet is to check either the Steam listing for a game (check the Deck Verified rating. Anything rated "playable" or "verified" should work pretty seemlesly on any Linux gamingPC) or https://www.protondb.com/ (a user run listing of the compatibility of different games. A good resource and often has some troubleshooting advice. Unfortunately it can often have outdated or just inaccurate information as it's all based on user reports. Still usually a pretty good indication of compatibility.) There's no indication on either regarding Starfield compatibility. Given that it's probably too resource intensive for the Deck it may not get as much special attention from Valve as something like Elden Ring (which ran better on Linux than any other platform after it was out for a few days and Valve had added a patch to Proton to fix an issue that the developers took longer to patch in the game itself.) Chances are pretty good it'll work though (assuming your hardware can run it.) The Steam page for Baldur's Gate 3 says it's Steam Deck Verified so it'll just work so long as you launch it through Steam. Here's the protondb page for reference https://www.protondb.com/app/1086940 . Crusader Kings III, Rimworld and Stellaris apparently all have native Linux ports so, while you may find reasons to prefer running the Windows versions with Proton, you don't actually need to check for any special compatibility. They just are Linux games.

Most of the Paradox games support Linux natively. I play Europa Universalis 4, Stellaris, Crusader Kings 2 (haven't bought 3 yet but it has native support), Hearts of Iron 4. Victoria 2 doesn't have native support and I didn't get Vic 3 but it is supported. Rimworld is native, so is Factorio.

Have a look at what you want to play on protondb.com and figure out if gaming on Linux works for you. Baldur's Gate 3 has a gold rating (gold being one level lower than platinum - the best rating for non-native games) which for all practical purposes should work.

EDIT: I recommend installing Proton Glorious Eggroll in addition to the native Proton on Steam if you can't get a game running with the native Proton despite protondb reports saying the game works. The installation is fairly straightforward, just read and follow the installation instructions on the page.