"Disable idleness checks when fullscreen" isn't supported under Wayland #442
Description
The reason is that idle_inhibit_unstable_v1 is not supported and we can't detect fullscreen. It will work by chance (if that setting is on or off doesn't matter though) because it's supported by Firefox, Chromium-based browsers, mpv, Kodi and Totem and some GNOME audio players. But Falkon, VLC, Strawberry and all others don't have it implemented. In fact playing a video on youtube inhibits idleness check also if not fullscreen. Afaik on x11 apps simulated activity to that purpose.
Probably there's not much we can do about it as only the compositor can detect fullscreen. The mentioned setting works fine instead with kwin_wayland (to recheck).
As the setting doesn't have any effect on Wayland we could just show it only on x11