I have the same issue when preparing my son's return. He had the proper amount withheld for both Social Security and Medicare and is unaware of any deferral. These amounts were correctly entered in TurboTax and yet the same advice regarding a corrected W-2 (W-2c) was issued. I can simply attribute this to software error. In any event, it doesn't affect the filing of the 2020 return as was correctly stated by TurboTax.
As an aside, my own State return was rejected twice due to what TurboTax admitted (and apologized for any inconvenience) were errors in its software. The third time was a charm and the State return was accepted without any changes to input on my part.
