I entered the "Filer's federal ID no." in the 1098-T section...do I need to enter it in a different field somewhere?
No.
That (school EIN) should be entered on the 1098-T screen.
It isn't needed on any other screen.
Did you import the 1098-T?
Please go through edit (for the 1098-T) and double check the entry on the 1098-T screen.
Try deleting the 1098-T and re-entering.
The American Opportunity Tax Credit DOES require a 1098-T and the school EIN which should be listed on that 1098-T.
I deleted and re-entered the Federal Id number, but nothing seemed to work.
However, during one of the many reviews I performed, the system showed the "real" form, and asked me to enter the school information, one page at a time. It asked for the ID #, which I entered again, and then showed a page to re-analyze my return for the credit to use. This time it managed to get us the higher credit (American Opportunity Credit).
I'm not sure how to trigger this manually, or find the form to enter this manually. In older versions of Turbo Tax, you could jump directly to the "real" forms and enter stuff in manually. This year's (2021) version doesn't let you do that.