TT should update their website information and the desktop software to explicitly state that you CANNOT e-file 1040X for years prior to current tax season.  Here it implies that you can:

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/e-[product key removed]-retur... 

Can I e-file my federal Form 1040-X amended return?

Your 2022, 2021, or 2020 federal Form 1040-X amended return may be eligible for electronic filing if the original return was successfully e-filed using TurboTax. However, there is a chance your return cannot be electronically filed. If this happens, you'll need to print and mail your tax return.