In the future, I encourage you to set the lower bound to gnome-shell (>= 47~)
The current version of gnome-shell in Experimental is 47~rc which sorts lower than 47 so this package is currently uninstallable in Experimental. gnome-shell 47.0 is expected to be released in a few days and we are waiting for it to be released and packaged before uploading any GNOME Shell 47 version to Unstable. So this issue will go away in a few days. Thank you, Jeremy Bícha
