Do I have to mail a 2021 federal return that has been E-filed and accepted

The option to amend your 2021 return isn't yet available in TurboTax Online.  It should be soon.

That said, it sounds like you made changes to your original return, which is an incorrect procedure.  Go back into your return and restore it to the way it was filed and accepted.  After you've done that, you can follow the instructions included in the TurboTax FAQ I'm linking below to amend your 2021 return.  (You'll see that 2021 is not yet available.)  

Your 2021 amended return can be e-filed rather than mailed.  This applies ONLY to current-year amended returns.  All other Forms 1040-X (amended return) must be printed, signed and mailed.

Please read the instructions and follow them carefully, as they are quite specific.

How to amend (change or correct) a return you already filed