The problem was that TurboTax defaults to 90% of last year's tax when it should default to 110% when preparing 540-ES estimated tax for next year. And the IRS rule is as follows:
"Individuals who are required to make estimated tax payments, and whose 2023 California adjusted gross income is more than $150,000 (or $75,000 if married/RDP filing separately) must figure estimated tax based on the lesser of 90% of their tax for 2024 or 110% of their tax for 2023 including AMT."
TurboTax should be defaulting to 110% of current year when calculating California 540-ES estimated taxes for the next year, not 90%.
TurboTax, please change your default to 110% when calculating 540-ES for California. I don't understand why the default is 110% for the Federal but not the State. Why? Please fix this.