TL;DR he used a “distress code” or something like that to wipe his local device.

If you have all of the photos, then you could use a tool like Immich Go, which would automate much of the tagging and album creation. I don’t know if Immich Go accounts for metadata from Synology. However, Synology might be able to export everything.

I would also recommend putting Immich remote access behind Tailscale (I.e., pointing the remove access server to your tailnet and using that domain name and the Immich port to login).