Since https://github.com/godotengine/godot/pull/108704, the sentence
about Flatpak is fully obsolete:
1. All standard Flatpak runtimes contain libdbus;
2. With the addition of support for the XDG Inhibit portal, Godot is
able to inhibit idle without any sandboxing adjustments.
More generally, I don't think we need to mention that D-Bus is required
to inhibit idle, even outside Flatpak: practically speaking, all desktop
Linux systems have had libdbus available for 20+ years.
Remove the whole paragraph.
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