that is a complex answer and without really understanding your use-case, no one can give you an answer.
but i can share some thoughts about how i handle backups of important data.
find the weak links
--- external hard drive.
--- using just a single application for all backups.
minimize dependence on those weak links.
--- use multiple tools.
------ local to local - use any backup tool
------ local to BB - use rclone
--- copy from each source to the final dest, minimzing use of the weak links.
------ copy source.A -> HD
------ copy source.A -> BB
------ copy source.B -> HD
------ copy source.B -> BB
with rclone, consider
--backup-dir with a timestamp for the folder.
copy using --immutable
lock down BB, use MFA, versioning and whatever else you can enable.