I retired near the end of 2023. Turbo Tax is saying that I will need to make quarterly payments in 2024 when my income will be substantially less. Why?

You can ignore them.  Just shred them.  The estimates are optional to pay and don't get sent with your return so the IRS won't be expecting them.  

You can ignore the Form 1040-ES payment forms for tax year 2024 if they are not needed.

You may get these vouchers if you're self-employed or had an uncharacteristic spike in your income this year. For example, you sold stock or took a large distribution from your retirement plan.

You're not required to make estimated tax payments; we're just suggesting it based on the info in your return. If you feel they're not needed for next year's taxes, you can shred them.