I have not received an answer but believe to have found it myself. Even though TurboTax did not print Form 6251 with my 2021 Return, it was contained within its dataset. So I opened the 2021 Return (with TurboTax 2021) and went to the Forms Tab. There, I searched for and found Form 6251, extracted the "alternative minimum taxable income" from the respective line and inserted it into the required field on Smart Check in TurboTax 2022. I hope this was the right thing to do. - Thanks
