I think this explains exactly where the bug is (for both Mac and PC versions)!! Developers at Intuit should certainly leverage this info for their debug
"Confirming, I get same error in TurboTax (Premier 2021 PC/Mac version) Form 2210, Part III, line 10, column A: required quarterly installment payment is twice what it should be. Probably left over from Tax Year 2020 when the first 2 quarters were rolled together by IRS. Hope this gets fixed in next TurboTax update."
