The mpv still appears not to “officially” support Gnome — the program prints this line to terminal with every video file:
[vo/gpu/wayland] GNOME’s wayland compositor lacks support for the idle inhibit protocol. This means the screen can blank during playback.
The screen indeed goes to sleep while playing a video on my system (doesn’t occur on Xorg), unless disabled in the ‘power’ options:
Is there a solution aside from running mpv with the