Okay so I figured it out after much experimentation. Here are my notes so hopefully someone won't have to do this. Couple of nuances that are really helpful.

Go to payments, penalties & extension - go to extensions.  For 4868 (federal) you can simply put in 4868 payment amount to be what you want/need it to be.

Click to state & local tab, enter your estimated income tax and tax withheld so it calculates the difference to be paid with the extension. Here, the "estimated tax payments" {override} is NOT the amount to be paid, so leave that blank. It works like a credit, not a payment.

Note - you cannot see these on the forms preview, you have to actually print the return and view the extension payments that are scheduled to be paid.  The full return is as of the tax return itself and doesn't (yet) reflect the extension payment as a deposit. Go to the 4868 form and your local state form to see the extension payment to be made matches your desired amount. In fact, the payment amounts on the original tax return (draft) are unchanged so ignore those - you aren't transmitting the return.

Last but most importantly. Once the extension has been FILED. Copy your manual payments to the payments "2024 estimated payments" tab to manually enter the amount paid with the extension so that it acts like a CREDIT when you finish preparing the final return. The extension amount does not carry here.

Hopefully this saves someone else a massive headache. Don't know why I can't find simple instructions anywhere else.

Laura