ask your lawyer. technically the law says no deduction nor taxability if "EXECUTED" after 2018 or "EXECUTED" before 2019 and modified after that date. "executed" is a legal term
you should find this link interesting
https://info.legalzoom.com/article/what-correct-date-divorce-date-filing-or-date-judgment-divorce
if it's concluded that you are entitled to a deduction, take it. you can inform your ex of what you are doing.
if you take a deduction and she doesn't report it as income, the IRS will eventually send you both a notice asking for proof of your position. the loser gets a tax bill.
