On Manjaro using Gnome 44 on X11 (linux kernel 6.3.5-2) the screen turns black after 30 seconds without mouse movement or keyboard strokes.
In Settings >> Power, I have set Screen Blank to ‘Never’:
With xset q, however, it shows me that screen timeout is set to 0:
DPMS (Display Power Management Signaling):
Standby: 0 Suspend: 0 Off: 0
DPMS is Enabled
Monitor is On
Also there it is set to ‘Never’. Interestingly it is also set to lock the screen immediately when blanks, which is not what is happening (after blanking occurs a mouse movement and a second of waiting is enough to return to the screen).
I just noticed that the problem vanished. I have no idea what caused it and what solved it. I am not even sure if there was a restart in between.
Interestingly xset q still shows Standby: 0 Suspend: 0 Off: 0, so that seems to be unrelated or overruled by gnome-settings.