welcome to linux. your screensaver is set to ‘none’. the display power management settings UI is set to never switch off the screen. and the screen switches off every half an hour. this is because the “real” settings are in 19 bullshit files somewhere, and they all override each other. because it’s linux you can edit all 19 files yourself, it only takes a couple of hours! but by the time you’re done there’s been a package update that resets your changes. it also changed the config file format