Thanks JamesG1, in following your advice I noticed that my understanding that TT was using itemized deductions was incorrect. At one point it said it was going to itemize, but it ended up giving me the standard deduction.
In trying to troubleshoot this I assumed that it was using the itemized number when I saw that the final deduction amount being used was $20,300, because I'd read that the standard deduction for HoH is $18,650. I didn't know about the age adjustment. I don't remember being asked about Cares donations, but I put $300 into line 10b and TT is happy now.
