The IRS wants me to re-attempt to e-file my 2021 return.

I think you misunderstood, since e-filing is permanently closed for 2021 returns.  The only way you can file a 2021 return is to print it, sign and date it in ink, and mail it in.

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.

Federal and state returns must be in separate envelopes and they are mailed to different addresses.  Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.

A 2021 tax return can probably be e-filed if you go to a tax professional (but you'll pay for that).  Consumer-level software can only e-file the current tax season.