Thanks for this answer even though it's very disappointing. Efiling is one of the important reasons I use TurboTax. Also, the system doesn't let you know about this functional gap until the very last step. I delayed several weeks thinking I just needed to wait until the new efiling season opened.
Given the IRS' minimal staffing, I now expect it will be a long time before they even look at my amended filing and other than my certified mailing documentation I have no proof of sending it.
