Backblaze has been supported by UNA since 14 beta. It has its own configuration in studio (s3 backblaze).

Your bucket must be set to public.

You must change configuration to s3 backblaze. You must manually move all files in /storage (use the s3 command line tool).

Then you must go back to the database and manually set all the ones that still read local to the s3 backblaze config. Because UNA does not copy files automatically, and will not change storage engines with files in the directories.

If you set everything, it will work.

Any setting but the s3 backblaze under storage will fail.