Deductions & credits

You are correct that, in this situation where DFAS will not pay your ex-spouse directly, you should issue a 1099-R to your ex-spouse.  Here's where the IRS advises that: General Instructions for Certain Information Returns (2024)  

Intuit does not support the issuance of 1099-R forms.  A couple of service providers that do support the issuance of 1099-R forms are TaxBandits and Tax1099 (not an endorsement).   

Ideally, the subtraction for the amount you paid to your ex-spouse would be reported on Schedule 1, Line 24z - Other Adjustments. 

If using TurboTax Desktop, switch to Forms Mode and on the 1040/1040SR WKS, look for Other Adjustments to Income Smart Worksheet, Line G and enter Nominee 1099-R and the amount (as a positive value).

TurboTax Online does not currently support this.  Instead, you would need to enter it as Other Miscellaneous Income with a negative amount.  Within the Miscellaneous Income, Other reportable income topic, answer YES to the question that asks Any Other Taxable Income?  Enter 1099-R Nominee and a negative amount.  It's going to be reported on Schedule 1, Line 3z - Other Income (as a negative).  Not ideal, but accomplishes the reduction of your total income.

Beware, if you have a state return that provides special treatment for retirement income, make sure it's not excluding / subtracting more than your portion of the DFAS 1099-R amount.  This may require overrides using TurboTax Desktop.

It literally will take an act of congress to get DFAS to honor QDROs for marriages of less than 10 years.  Here's an excerpt of a DoD recommendation to Congress from 1999, which to this day, hasn't been acted upon.