What should restic do differently? Which functionality do you think we should add?

#5449 has added support for restoring file ownership by name. However, this does not work for POSIX ACLs so far. For those restic currently only stores the uid/gid but not the corresponding user and group name on the source system.

Fixing this requires extending the repository format to also allow storing the required information. Then the POSIX ACL xattrs can be rewritten on restore. (See borgbackup for a possible implementation of that).