You claim that Steam does not come with Proton on regular Linux distributions but you’re wrong which is an easily googlable fact you continue to deny.

I continue to deny it because it’s wrong. I don’t know what Google says, I just know how it worked when I used it myself.

At most the “Enable Steam Play” checkbox has to be ticked in Steam’s settings.

Which is something it does not tell you and does not tell you how to do.