Old games are likely to work better, as new games are likely to use new features or behaviour which aren't yet handled properly by Wine/Proton.

Check protondb for reports on whether a specific (steam) game runs.

In my experience, pretty much everything that doesn't have anticheat works. I can't remember the last time a game didn't work fine, from stuff so old it stopped working in Windows Vista to day 1 AAA titles. Even DOS stuff is playable with DOSBox.

Just be aware, Linux is not windows. If you try to use it like windows, you will only experience pain. It's not hard, especially with mainstream distros like Ubuntu or Mint, but you really should invest at least a bit of effort into learning how the system works and how to use it properly.

Proton is amazing. There are several games I've played on my Linux laptop that have Linux versions, and they don't run as well as playing it with Proton.

Check out protondb

As long as the game isn't a title thats using something bleeding edge, it will work day one. And as long as the game isn't using an non proton compatible anti-cheat, it should work. Unless said devs arbitrarily decided not to tick the "proton compatible" box cause of some hard-headed bullshit.

I would say old games work better also get Steamtinkerlaunch which makes fucking around easy

If the game isnt steam just add as non steam game and bang steam will handle the rest

I had great experiences with old games on Linux. Mostly they work better than on a modern Windows system. For Example Neverwinter Nights 2. Under Windows movement is jittery on fast CPUs. There is a community patch for that thankfully. Under Linux it just works with WINE (the patch is advisable for other reasons there too). Also loading times are blazingly fast under WINE and Linux. On my HDD PC 1 second vs 50 on Windows. Now with a NVME SSD, Windows also only takes 2 seconds.

Of course Wine/Proton is not perfect, I still have a dualboot system for that. But I boot to Windows very rarely these days. When I do I am hit with so many slow updates, that I don't get to my game. Maybe I should stop doing them and cut of its network access.

Really old games tend to be more difficult. For a relative I set up a VM with Win98 as the performance impact won't hurt the games, some even benefit. (I believe the games where Safecracker and Theme Park) Even older than that DosBox and ScummVM work perfectly.