Why is not 100% of my State overpayment being applied to 2021 State estimates, instead of giving me a refund?

You have a choice of what to do with your state and federal tax refund with respect to having it applied to next year's tax or receiving a refund. You should review your state tax return and you will see an option to choose what to do with your refund before you finish up your review.

......or if you had already indicated amount to apply to 2021 earlier this week or in the last few weeks...last night's software update may have changed either your Federal, or your state form calculations, and the resulting state refund amount.

Which is why some of us drum-beat regularly pleading with people to not file their taxes before all the forms have been fully updated, and some states are STILL in flux for another week or three......sometime AFTER the IRS starts processing.

It sounds like accidently selected to have your refund applied to next year's return.  if so, you need to change it.

The state programs may vary.  On my state, it's found on the screen titled "A Few Things Before We Wrap Up your State Taxes".  Look for "Other Situations", then "Apply your refund to next year's taxes".   Click on Revisit or start.

If the opposite is true, you want more of your refund applied, you change it in the same place.