In the new Furtherance based on Iced (v24.10.3), the idle detection on GNOME only works as supposed when Furtherance's window is visible, i.e. not minimized, fully hidden behind other windows, or moved to a workspace other than the currently active one.

I tested with Bluefin (bluefin-dx:gts which is currently on GNOME 45.6) and Ubuntu 22.04 (GNOME 42.9), using the Flatpak.

The old Furtherance built on libadwaita didn't have this deficiency, i.e. idle detection under GNOME reliably worked regardless of the window state.