I tested in “Backup with eRecovery? - #6 by tcecyk” what an /e/-recovery adb has in capabilites and used it to backup/restore the userdata partition on the same device, but see the details concerning partition layout and encryption. Would you consider testing this approach? it will not be space efficient though, copying the full partition
Seedvault could ease the move to a higher major… the integration can happen with later versions so if there is overlap for another version of 0.19-q and 0.19-r for the same device, it is a possible migration path.