When set to Sync, which should delete files from B2/remote storage when they are deleted locally, files instead remain in the B2 bucket.
NAS-103212, however, I believe the conclusion there was incorrect.
While it is true that B2 errs in the direction of retention it can be configured for deletion and FreeNAS appears to not be doing what is required to allow for that function. I believe the implementation of API calls b2_delete_file_version (https://www.backblaze.com/b2/docs/b2_delete_file_version.html) and/or b2_hide_file (https://www.backblaze.com/b2/docs/b2_hide_file.html) is needed. If delete isn't working then hide is the way to go as B2 Lifecycle settings can be configured to remove files that have been in a hidden state for X days. A quick consult with someone at Backblaze should be able to sort out the most efficient course. I have other solutions such as CloudBerry backup that have no problem deleting files entirely from the B2 store so this is not simply a B2 limitation.