@wfk If you're open to trying something really different but Linux-focused, there is my hand-coded project Wyng backup which is now receiving development support from Qubes OS.

Wyng can backup data in a small fraction of the time vs what rsync or borg can achieve because local data does not have to be re-scanned/checksumed to find changes (the catch is that source data must reside in compatible CoW storage, although there's no such requirement on the back end).