By default only the officially supported games are listed. If a game is not supported this does not in.any way mean that it will not work. In my experience everything except some anticheat infested games will not work. For some rare games some tinkering is necessary, yiucan typically find infos here in the protondb
To make all games visible, go to your settings then go to the “Compatibility” settings, then locate the “Steam Play” section. Toggle on the “Enable Steam Play for all other titles,” choose the latest Proton version from the dropdown menu, click “OK,” and restart Steam.