Yes, you can either add the game as a non-steam game and force proton, or use Lutris or Bottles (with proton or other WINE runner). For repacks with installers, you can launch the setup.exe with Lutris or Bottles (install the game to 'fake' drive_c and move it), just make sure you include dependencies that require it (usually .net framework).

Source: most of my steam library on my steam deck is plundered loot

Linux is paradise when it comes to emulation 🎮

not purchase games?

😏

Lutris is good for that. It can be confusing at first if you don’t know how Wine works, but it’s very easy to use and doesn’t require Steam.

Sure. I've run several modern ... repurposed... games and it usually works through lutris.

At this point in time, I only occasionally have mild issues with newest games, because Wine is a continuously developed software, and games with an annoying anticheat, such as Destiny 2 or R6 Siege. Everything else just runs, including older games, that don't even run on Windows, or titles you had to sail the seas for

Yes, Steam doesn’t do anything

You can just as easily use Wine/Proton as your runner as you can set up Steam to use Wine/Proton as your runner

yes but steam is so easy

Yes, but it will take some learning time

Yeah it’s great. Bottles is the best tool imo, lutris almost feels like a relic from the early days of Linux gaming, and non-steam games in steam don’t always work exactly how you might want, and aren’t so much fun. There is also heroic games launcher now which lets you add custom games and is also a very nice option if you don’t use gnome (bottles is a gnome style app so it may look out of place elsewhere). I would put some thorough research into VPNs if you torrent though because the one I used on my Linux box (expressvpn) leaked my ip at some point and I got a letter in the mail.