This Form 1099-R should have been reported on your 2023 tax return. If the amount from box 2a was not included on line 5b of your 2023 tax return, you must amend.
You should not delay amending since doing so will only cause you to have to pay more in interest and late payment penalty. Since the IRS will not yet have the 2024 Form 5498 from Fidelity reporting the rollover to the Roth IRA, your explanation required to be included on Form 1040-X will suffice. The IRS will bill for the interest and late payment penalty on the balance due that you'll be paying with the Form 1040-X.
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