Following the answer here: Missing AACS configuration file" error when playing blueray movies but am still getting the exact same error.
Ran with logging:
keydbcfg.c:680: No valid AACS configuration files found
aacs.c:121: No usable AACS libraries found!
dec.c:197: aacs_open() failed: -2!
It would have been nice if they had put the file they were looking for in the log...
Anyway, I have placed the file in .config/aacs/KEYDB.cfg and sym linked it to snap/vlc/current/.config/aacs/KEYDB.cfg.
Not sure what to do next.