@DecaTec your skript works as well with lxd? e.g. is it the same command to switch maintenance mode.
i don’t know lxd but in docker it wouldn’t.
millions of apps can backup anything on linux. 
it’s a bit out-dated but still might work: Nextcloud Backup and Restore - #6 by Reiner_Nippes
here’s another article on backup/restore: URL REMOVED - Spam-protection [JK]
@Bahman but you have to adapt this to your lxd environment. ok?