I made progress on part of this. Regarding problem (a) in the OP, I found out how to find the "Schedule D AMT" for 2021. I'm using TurboTax for Mac. I couldn't find the form because it's not listed in left panel of the Forms view.
Indeed, it does not appear in that bar. But I was able to find the form by clicking "Open Form" in the toolbar, then typing "Schedule D AMT" in the search box, then opening the the form from the list in that dialog.
When that form is opened, I see that it is filled out. Further, I see the values on Line 7 and Line 15 are what I expected; NOT equal to the crazy number that TurboTax claims to have imported automatically. Therefore, I'm now even more convinced that there's a bug related to problem (b). That is, TurboTax is "importing" numbers out of thin air instead of properly pulling the numbers from last year's "Schedule D AMT".
