Also be sure your snap have access to something else than /home
by connecting them to the removable-media interface.
You wouldn’t need to face those AppArmor things and limitations about symlinks if you only moved the /home/$USER/{usual_folders} to another location ( instead of moving the whole /home or /home/$USER folder )
See Symlinked $HOME break snaps Ubuntu 20.04 (Solved) as an example.
@lucyllewy and @ogra : I don’t understand why you advice such complicated things when there are easier and simpler ways to achieve a good result without modifying the root tree of system ?
Just keep /home/$USER at its usual place in the / tree, but move parts of its content elsewhere and symlink or bind those. Or is this something that may get impossible to do later ?