As a last resort, try deleting the Form 1099-R for the distribution and also delete the information about your Traditional IRA contribution.
Then save your return and get back into it. Go directly to the Traditional IRA contribution section and follow the steps outlined by macuser_22 or the steps in the TurboTax article below. The order that the data is entered is important.
How do I enter a backdoor Roth IRA Conversion?
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