If your kwallet store file is gone, that is a real problem. I’d be surprised if that happened by an upgrade, Upgrades aren’t supposed to delete personal files, AFAIK.
As noted, our snapper as shipped does not support XFS snapshotting, but it can be done… Google “XFS snapshotting” for the many articles how it can be done.
The main idea of rolling back your root partition (if the fs is BTRFS) is to restore the kwallet4 application so that your password store might be readable again (of course your password file has to exist).
I would expect if you copied or backed up that file <anywhere> and restored or copied the file to your system <and> roll back your system could allow you to open and extract the file contents.
TSU