I've used TurboTax for many years. I'm currently in the process of filing amended returns for 2019, 2020, and 2021 because TurboTax did not properly calculate the California mortgage interest deduction. And TurboTax's instructions are poor. I've now spent many hours fixing errors.
Make sure that you look at the CA Adjustment Worksheet for your CA return. In my case, instead of adding the difference between the Federal deduction and the California deduction allowed (which results in a larger CA deduction, thus lowering the amount of tax owed), TurboTax subtracted the difference (exact opposite of what the software should have done). This caused me to pay more CA tax than I should have.
And TurboTax seems to have a hard time handling mortgages greater than $750k that were refinanced after 2017. I think I'm allowed to deduct up to $1 million of interest because my original purchase mortgage was prior to 2017, thus the refi is "grandfathered" in up to the $1M limit.
