Can I apply my refund to next year's estimated tax? It shows direct deposit, check, and split, but not apply.

Yes. From the Federal menu, choose Other Tax Situations. Expand the menu for Additional Tax Payments. Click Start/Revisit next to Apply Refund to Next Year. 

How do I split my refund between an estimate and partial refund

Please see the below TurboTax Help Article for assistance with applying a portion of your refund toward your estimated taxes:

How do I apply my refund to next year's (2021) taxes?

@Edward315