Steam Launch Option
Instead of using Steam Tinker Launch as Steam Compatibility Tool (recommended) it is also possible to use it as Steam Launch Option
To do so, just add it to your Steam Game Launch Option command line like this:
stl %command%
For every game using any Compatibility Tool, Steam downloads the Windows version, so if you want to use stl with a linux game, use the Steam Launch Option!
When using the Steam Launch Option, changing the Proton version from inside stl is disabled as it conflicts with steam internal game start mechanisms. This might be "hackable", but keeping it clean is preferable. Also this is the only way to use only Steam for configuring a Proton version without any additional configuration needed.