"su - non-root" arises "su sorry"
From the macOS User Guide (more specifically the description of sharing-only users):
Sharing-only users can access shared files remotely, but can’t log in or change settings on the computer.
A sharing user has neither a home directory (run ls /Users to check) nor a login shell (dscl . -read /Users/sharingiscaring UserShell returns UserShell: /usr/bin/false).