Technology

Adding to what the others were saying, proton has an unaffiliated website for reporting purposes, protondb.com. It tallies user reports of the games working or not. The data is associated mostly with steam libraries.

I don't have a lot of games in my steam library, relatively speaking, barely over 100. But there are zero games that would not work on Linux for me:

In this context Platinum means it works out of the box, Gold means some users experienced minor issues (mostly older reports by nvidia users) that required some tinkering with launch options, such as setting an environment variable. Silver and Bronze mean gradually more tinkering required but still works. This excludes native apps (which do not use wine/proton) and borked apps (of which I own zero).

Note, that this is a translation layer, not emulation, and often games can have better performance under Linux thanks to the system not getting bogged down by the OS itself.

Also note, that 99% borked games are due to kernel level anticheat and DRM being implemented improperly by the game developer, which proton can't handle. You can still make it work under Linux, but you'd actually require emulation for that, instead of proton.

Edit:

Another screenshot of the top50 played saturation to show you what to expect.