The vanilla-gnome-default-settings package does not revert the Ubuntu background/screensaver images to gnome behavior in 22.04.
vanilla-gnome-default-settings contains the file /usr/share/glib-2.0/schemas/20_vanilla-gnome-default-settings.gschema.override for reinstating most gnome default settings. The keys org.gnome.desktop.background.picture-uri and org.gnome.desktop.screensaver.picture-uri currently point to the file /usr/share/backgrounds/gnome/adwaita-timed.xml, which was removed from the gnome-backgrounds package in 22.04. The removal appears to be related to a change in the way Gnome 42 handles background images in the context of light/dark theme preferences.
gnome-control-center seems to be in a halfway migrated state between Gnome 41 and 42, so I'm not completely sure I understand what the right fix here should be... Simply updating the keys to point to (what appears to be the new equivalent file?) /usr/share/gnome-background-properties/adwaita.xml doesn't change anything. I think a minimal (short term?) fix is to set
[org.gnome.desktop.background]
picture-uri='file:///usr/share/backgrounds/gnome/adwaita-l.jpg'
picture-uri-dark='file:///usr/share/backgrounds/gnome/adwaita-d.jpg'
There is not an equivalent 'dark' version of the key for the screensaver portion, though... There are also some new 'primary-color', 'secondary-color' keys which should probably be considered (their upstream gnome values appear to be '#023c88' and '#5789ca' respectively).
