I agree with your assessment of Intuit's apparent attitude about this situation.
But TurboTax Advantage 2021, which I'm using, did not automatically calculate the difference between allowed Fed and CA mortgage interest deduction. I went to CA FTB's website and read what is necessary to adjust between the two amounts (actual interest paid vs federal limit). Then in TT, I went to the CA form Schedule CA, found the line on which to enter the additional amount of interest I paid (line 8, column C), and manually entered it myself. That appears to have worked.
And as you mentioned, I now need to amend tax years 2018 - 2020 with California, because I've overpaid each year, which amounts to thousand of dollars.
