Thank you @MonikaK1 for your response.
I did make the Q1, Q2, and Q4 payments in the correct amount on the correct dates to meet the 110% payment of my 2024 taxes owed. And I continue to believe that the calculation of Line 5 is in error.
However, I discovered that California has a "new" law requiring payment of 90% of THIS year's tax if your taxable income exceeds $1M. (A new situation for me this year.) Since I've never exceeded that threshold prior to this tax year, indeed I have underpaid the required amount.
However, I don't believe that Line 5 should reflect that and I still believe the calculation for Line 5 is incorrect. Line 6 is where this should be addressed. There it says: "Required annual payment. Enter the smaller of line 2 or line 5. (If your California AGI is equal to or greater than $1,000,000/$500,000 for married/RDP filing a separate return, use line 2)"
Again, the Line 5 calculation is incorrect but in my case I don't believe it will affect the overall calculation of any underpayment because Line 6 correctly uses the number from Line 2. Note that TurboTax has filled in Line 5 with the same number as Line 2 for some reason and I believe that is an error, but it does not affect my outcome.
I will file my taxes and let the state determine what, if any, penalty I owe.
