At this point it’s failing to wake up after suspend (EDIT: The fans spin up, and the screens wake up but they’re black). This happens whether I suspend using the Plasma app launcher, a keyboard shortcut set up from Settings, or systemctl sleep
I also tested that as root since you pointed out the permissions issues. Still got the same issue, but the journal has this a bunch of times:
Sep 30 08:28:23 Marvin kwin_wayland[1415]: kwin_wayland_drm: Setting dpms mode failed!
Sep 30 08:28:23 Marvin kwin_wayland[1415]: kwin_wayland_drm: Atomic modeset test failed! Permission denied