To complete your 2020 return, you will need your Recover Rebate Credit(s) received. The credits are not taxable but need to be known to determine if the amounts you received are correct. Claiming the Recovery Rebate Credit's wrong amount will cause the return to require additional IRS review, which will delay refund processing.
You can confirm your stimulus payments either by referencing IRS-mailed Payment Confirmation Notices 1444 and 1444-B, checking your bank account activity, creating/viewing an online account, verifying issued payments through the Get My Payment tool, or requesting an account transcript.