In 2020, there is no alimony deduction. In 2018, the alimony deduction that was available was the same that had been part of divorce planning strategies for over seven decades. The deduction had allowed the ex-spouse paying support to deduct it on their taxes. That gave them a tax break. The ex-spouse who received it had to pay taxes on it. That shifted income from a higher tax bracket to a lower one, in many cases, which meant that more money stayed in the family.
Now, that deduction is gone completely. Only divorces that were finalized prior to 2019 retain the tax status, but those after 2019 don't have the same tax benefits. That only considers federal taxes. States sometimes allow deductions and taxes, but not all do.