I checked with support and they informed me there is a 5 GB size limit with the product - because of an older 5 GB limit on the B2 side.

Once thing you can try (I have not tested this so cannot confirm if it will work) is to create a B2 bucket as S3 Compatible (on the B2 side).Refer to this post about how to do this. https://kb.msp360.com/cloud-vendors/backblazeb2/backblazeb2-as-s3compatible

Then create a new storage connector in Explorer using S3 Compatible:
You may need to select Version 4 Signature when setting up the account in Explorer.
Select the option to use native multi-part upload.

Do a test on a large file to see if we use the multi-part API to move the file to B2. Do a test copy from B2 back to local.