You can file an extension.
IRS extensions for tax year 2021 must be filed on or before April 18, 2022 for domestic taxpayers.
It isn't possible to file a post-deadline extension.
Keep in mind: An extension doesn't give you extra time to pay your taxes — but it will keep you from getting a late filing penalty. (You'll still owe interest if you pay after the deadline).
Note: If you're paying additional taxes owed with direct debit, you'll need to provide your 2020 AGI for verification purposes (if you didn't file a 2020 return, enter 0 as your AGI).