Hi, thanks for replying.
I did try to update again after having created that missing directory, but it didn’t help.
I noticed the error complains about this being a missing source directory, not destination directory for the backup, so the cause of this error must be somewhere “deeper” in the installation.
Likely I’ll have to reinstall my whole YunoHost server anyway, because the migration to 11 doesn’t work (see my other issue posted at Migration fails: 21. Upgrade the system to Debian Bullseye and YunoHost 11.x). That will then also resolve this Vaultwarden update issue …