I spent two hours today trying to figure out why Nextcloud couldn’t read my data directory. Docker wasn’t mounting my data directory. Moved everything into my data directory. Docker couldn’t even see the configuration file.
Turns out the Docker Snap package only has access to files under the /home directory.
Moral of the story: never trust a Snap package.
Snap sucks, but not for the reason OP stated. There’s a decillion reasons for why Snaps suck, why make up a reason that applies to other formats that are actually good?