Lockitdown's solution worked for me. I'm not a tax expert. I read IRS publication 936. On page 13 of pub 936 the directions for calculating the average balance is explained, and it lines up with this solution.
I also figured out how to edit the forms on the Mac CD version of TurboTax - you have to go to the form, click on the box you need to change, then go to the Edit menu and select 'override'. I did not have to fix the box on Schedule A - once I corrected the average balances of the mortgage everything propagated through the forms and worked correctly.
I don't understand why TurboTax still hasn't fixed this bug, but I imagine it is effecting millions of people that refinanced in 2020 to take advantage of the historically low interest rates.
