Why am I getting this message? Since you deferred some of your Social Security taxes last year you will get Form W-2c. I did not defer any taxes last year.

If you got the message  "Heads up! You have a W-2C coming" .  This was fixed in the newest release on 2/19/2020.

Only the customers who now legitimately will receive a W-2C will still get the pop up.

A W-2c form is used by the United States Internal Revenue Service for tax filing and reporting services. This form is known as a Corrected Wage and Tax Statement form.

Is that true for the Mac version, too? I just got the message after updating and did not defer Social Security taxes. 

Review you W-2 input screens.  Make sure the Social Security taxes in box 4 are 6.2% of Social Security wages in box 3.