So the CP28 is just a warning at this point.
https://www.irs.gov/individuals/understanding-your-cp28-notice
It sounds like turbotax claimed $36,601, and using the two different methods in Publication 936 gives you $36,024 or $36,559.
For $42 of deduction (probably owe $10 more tax) I would think about ignoring the issue and wait and see if the IRS sends a stronger letter. But it's your neck and you might want professional advice.
Or, you can file an amended return using the figure $36,559, and explain in the reason for amended return that you recalculated the deductible mortgage interest using the interest rate method in publication 936. But as mentioned, to file the amended return with turbotax, you either have to provide false answers in the mortgage interview to get the calculation to come out correctly, or you need to use the Desktop version of the program to prepare the amended return, and enter the correct amount of interest directly on the tax form using the Override method. I would try calling customer support to ask for a copy of the 2024 software to install on your own computer because you need to file an amended return with an override.
I will flag this for attention just in case. Can you go to the support menu and locate "Send file to agent"? This sends an anonymized version of your file to tech support and gives you a token number. Post the token number here, that can be used to link your concern to the uploaded anonymous file.
