Are you using multiple screens and have something open on another screen that periodically rerenders? I have had a similar problem when having Ksysguard open on a second screen - every time the graphs rendered a new time step, my game lagged. Only happened on Wayland. My solution was to run the game inside of gamescope or to close the offending application.

Yes, you can either add external games inside steam and set their compatibility options to use some version of proton or use proton through lutris or manually.

Chrome […] is spyware. Don’t use chrome.