About the only way to reduce 2022 taxable income in 2023 is to make a deductible traditional IRA contribution or an HSA contribution, if eligible. Keep in mind, though, a deductible traditional IRA contribution just defers taxable income to some future year and will be taxable when you eventually take that money out of the IRA. If your marginal tax rate in the future is not expected to be less than it is now, you might as well just pay the taxes now.
It makes no sense to take money out of a retirement account just to make a contribution to a retirement account. To be of any benefit, the money would have to come from somewhere else, say, the severance payment.
Bonuses and severance pay are supplemental wages reportable on your W-2. Tax withholding might be calculated differently on bonuses and severance pay than it is on your regular pay, but in the end that usually doesn't matter much because your tax liability is unaffected by the amount of your withholding unless under-withholding results in an underpayment penalty.
