I take my RMD distribution in Dec. I pay my estimated tax on it then. Turbo tax thinks I got the RMD all year. A late payment is assessed. How do I avoid this issue?

You may be able to eliminate it.  You can go to Federal Taxes tab or Personal tab, under Other Tax Situations and select Start by the Underpayment Penalties. You will answer a series of questions that may reduce or eliminate the penalty. Or you can elect to have the IRS figure the penalty for you.  It's form 2210.

It's under

Federal or Personal (for Home & Business Desktop)

Other Tax Situations

Additional Tax Payments

Underpayment Penalties - Click the Start or update button