Enter/space are already taken over by the app icon to activate the
app, and arrow keys interfere with keyboard navigation where icons
are arranged in a grid (namely the app picker).
Also as app icons only create the menu when it is first needed, the
shortcuts only starts to work once a menu has been opened, which is
rather inconsistent and confusing.
It is better to simply disable the key handling altogether for the
app icon menu.
https://gitlab.gnome.org/GNOME/gnome-shell/issues/98
035dfe2a19