TIME MACHINE BACKUP KERFUFFLE
  1. Time Machine will only backup to drives formatted HFS+ and not to an APFS drive
  2. Time Machine will not allow backups from an encrypted APFS volume to an un-encrypted volume
  3. Time Machine and DiskUtility both support encrypted HFS+ volumes
  4. At this juncture Time Machine automatically excludes APFS (Encrypted) volumes from backups and unless there is a secrect key to the kingdom I have no yet discovered they cannot be removed from the list of excluded items.
    mad confused mad
(Sorry Artie but emojis are the only adequate way of expressing my opinion of this Catch 22.) I keep saying to myself, "Self" — that's what I call myself when I am muttering under my breath — "this is an early beta and you've been down this road before. Lets make that my third High Sierra Feedback report." But I really want to express myself in stranger language than that.

Surely this will be caught and fixed.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein