Is running a personal relay really the best solution for nostr backups? Surely network traversing is a non-trivial issue whenever you're not on the same network as your PC? Aunt Beth is not going to use tailscale. Wouldn't something like https://nostrsync.live, perhaps running locally and with some backup automation, be a better solution?
Discussion
a relay could be configured to look at other relays for events and download any missing events. this is already the case for Umbrel's relay.