You should not file for an EIN prior to registering your business name with your state in case you cannot use the name you plan. In your case, it depends if you filed for your EIN as a C Corp or if you filed as another entity (like an LLC) that is electing to be treated as a C-Corp.
If you filed for your EIN as a C-Corp then you need to file a 2021 tax return because you had an EIN and use your correct Incorporation Date. You will need to file your return by mail in this case as the e-file system will not accept a return for 2021 with an incorporation date after year-end.
If you received your EIN as another business entity (like an LLC for example) and your incorporation date is the date you elected to be treated as a C-Corp, then you do not need to file a return for 2021.
See Who Must File from the Instructions for Form 1120 for more information.
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