Hi Brainstorm, 

This is a new tax deferral (temporarily) of the part of the SE tax corresponding to the part of the Social Security portion. Many tax professionals are cautious about this because it will have to be paid in 2021 and 2022 and it could cause a higher tax burden for many taxpayers. Just be cautious, it may reduce your tax  this year but it can increase your taxes in the near future. But you are right, the software will ask you, I and many professionals I have spoken to, will enter 0 on Line 18 so nothing will change. Hope this helps.