Retirement tax questions

Sorry, but I can't make sense of it.

I got all the income, including what my ex-spouse should have gotten.  OPM has withheld income tax based on that.

Now I'm ordered to give my ex $8,029.  That will be coming from the total income I received from OPM, which has had income tax withheld.  [I'm not even concerned about my ex's income increase that probably is not going to be reported (under the table, so to speak)].  When I report my net income (gross minus income tax withheld, which will be reported on the Form 1099R from the OPM), why am I not able to report the $8,029 payment as ordered to my ex?

I can tell you that the partial arrears payment the OPM did make to my ex had an income tax withheld.  That partial payment will be deducted from my monthly annuity payments spread over the next two (2) years.  Therfore, that parial payment will not appear as income for me.  That partial payment won't be reported when I file my income taxes for both Fed and state.  So why can't I deduct $8,029 from my 2024 income, similar to the effect of the OPM partial payment to my ex?

I appologize for my confusion, but I hope you can simplify it for dumb me to comprehend!

Thank you for your assistance, it is greatly appreciated!