I recently bumped the desktop PC with the scanner from an old Mint to Xubuntu 18.04, which killed a day with all the system and UI tweakage.
The old guides for setting up a networked SANE scanner became inoperative with
systemd ruling the configurations, so, after some flailing around, I found a newer guide referencing a guide for USB scanners and pointing to a deeper guide for network sharing in the age of systemd.
The USB guide points out the existence of Access Control Lists for the various device files, which I didn’t know was a thing. AFAICT, you must still be in the
scanner group for remote access to happen.
I lost track of the changes during all the flailing around, but it definitely didn’t Just Work.
I’m sure all this will change before I must do it again.