Since you did not even know of the existence of the bonds until 2021, you can report the interest income on your 2021 income tax return. I would keep documentation to support your discovery of the bonds and the subsequent interest income from initial purchase until the date of maturity.
Your 1099-INT will most likely be issued for the 2021 income tax year and therefore, you would need to match the year it is reported to the IRS to your personal tax return.
Please see the link below and see the section titled Reporting the interest all at once at the end for more details. It does state a 1099-INT will be issued "early the next year" for any bonds redeemed.
Reporting redemption of bonds
IRS FAQ for reporting savings bonds
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