I am in the same boat. TurboTax Business 2021 tells you that for e-filing you must include the Rental Real Estate Enterprise Statement (Safe Harbor Statement) as a PDF attachment. I assume this is because it must me signed. Then there is no way to attach this PDF to the return for e-filing that I have found. As you stated, the only PDF attachment allowed is the Form 8453-PE. One would think that under the "Attachment" tab that there would be a way to add PDF attachments, not just view attachments.
For 2020, TurboTax Business allowed the Rental Real Estate Safe Harbor Statement with the name printed, so there was no need for a PDF.
