Piracy: ꜱᴀɪʟ ᴛʜᴇ ʜɪɢʜ ꜱᴇᴀꜱ

A significant number of games on Steam can literally just be ctrl c ctrl v'd into another directory, snd still more or less work, or be made to work if you ... configured Proton through Not-Steam,.for them.

Mostly only games on Steam that have some kind of always online DRM are going to throw a shitfit in that scenario.

People seem to forget that Steam and Source were built from the ground up to support what is I guess now the 'old school' way of modding a game: you just literally throw more shit into the game directory, edit what is already there, etc.

You can add /any exe/ external to Steam, to Steam, and run it via Proton. ... /any exe/.

I've managed to get fucking Cascadeur working on Linux, via Steam/Proton, lol... there are a few games I tinker with where the model or anim ripper scripts only work on Blender 3.6 for Windows... So, download Win Blender 3.6, add to Steam/Proton, run, install Windows only plugin. Voila! Bit of jank, but it does work.

Any game that somebody has figured out how to do the equivalent of... some kind of script extender, to enable mods to do more kinds of stuff?

The way those work is they basically hijack or replace the original game exe.

Any game that has been reverse engineered to this extent, you can get to run independent of Steam.

I've done it with CyberPunk 77, NewVegas, etc, toying with my own mod making attempts. Its not too hard to futz with configs and launch arguments to launch straight into the main CP77 exe, just skip the launch/loader thing.

You can actually just do this kinds shit for quite a lot of games.