I've been using Linux more and more recently but one thing that annoys me is my EndevourOS thinks the PC is not in when I'm playing games via a gamepad, therefore dims the screen and tries to sleep. How do I fix this? I'm honestly surprised I even need to.
KDE? You tried "Systemsettings > Power Management > Energy Saving > Dim Screen" maybe already? I don't have what you're describing either und Arch nor Endeavor.