The tax is due in the tax year you make the conversion (when it's completed - funds transferred from IRA to ROTH). It's late in 2023 so if you tried to do it before the end of 2023 it might not be completed and hence taxable until 2024. Check with the IRA custodian. There is no requirement to convert 100% of your IRAs to ROTHs in one year. It's all about tax brackets so spreading the conversion out over 2 or more years may save you some tax $s.
