I had $1729 federal refund pending w/ $13,000 itemized deductd. So, chose std deduction $26000. The $1729 didnt go up. How is that possible when deductions doubled??

Are you filing Married Joint, and both over age 65?

Yes.

TurboTax is optimized to get you the maximum legal refund. The default setting is for the Standard Deduction, before you start entering itemized deductions. Any refund or tax due showing is based on the Standard Deduction, until you have entered enough itemized deductions to exceed the Standard Deduction.

In your specific case, the $1729 federal refund was based on the assumption that you would file using the Standard Deduction, even as you were entering itemized deductions into TurboTax. Only if your itemized deductions totaled $26,001 or more would you have seen a change in your  refund.