Try reviewing your entries in the Traditional IRA contribution section. If the conversion is showing as taxable, then the Traditional IRA contribution may not have been non-deductible.
You can also take a look at your Schedule 1 line 20 to see if it has a value there or if it is blank. If there is a value, then the Traditional IRA contribution is being deducted when it shouldn't be.
Review the instructions again, paying close attention to step 1 of the process:
How do I enter a backdoor Roth IRA conversion?
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