Maybe there’s some interplay between amd64 and x64 architectures.

AMD64 and x64 are the same thing. Do you mean AMD64 and x86? There is definitely interplay there, as AMD64 implements the x86-32 instruction set.

Same — rsync to a pi 3 with a (single) ZFS drive at family’s house. Retain some daily/weekly/monthly snapshots.

I have a (free) VPS with static IPv4 which is how I connect everything.

Both the VPS and the remote site have limited network speed (I think 50Mbps for VPS), so the initial sync was done sneakernet (well…“airplane net”). Nightly rsync is no problem bandwidth-wise, and is mostly just any new videos I’ve uploaded to my local Immich instance.