I use Longhorn for generic PVC and static NFS shares for large files. Longhorn creates scheduled backups to a NFS share, which is then backed up to a Backblaze bucket. I have yet to test restore from Backblaze tho :D
Of course this means that I have 3 copies of the same data across multiple Nodes because of how Longhorn works. That's why I usually don't create large volumes, just enough to get the app working
I have been using Authentik for several years now, works great with k8s. Not sure about the difference between Keycloak and Authentik tho (feature vise)