It's too late to efile 2020 or prior. How do you know it wasn't filed? If you need to file it now you will have to print and mail it. It probably did get filed. The IRS is still processing 2020 returns. Did you try entering 0 for the AGI to efile 2021?
Did you use the Online version or the Desktop program? When you efiled did you get back the Accepted email?
If you used the Online version, When you log into your account you should also see the status and if it was Accepted or Rejected, Started, Printed, Ready to Mail, etc. what does it say?
You can now check the IRS IRS Where's my refund to Look up prior years.
