No, you don't need to file the 2020 Form 1040-X since it seems that the taxable part was correctly shown on line 4b.
You can file the 2020 Form 8606 by itself.
Technically you can be fined $50 for failing to file the form on time, but the penalty can be waived if you have reasonable cause. Please see Relief for Reasonable Cause for additional information.
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