Hey, Lisa, One of my clients got an underestimated tax penalty that's related to this issue.  He had the option to defer his 2020 SE tax but chose not to.  Proseries calculated his 2021 estimated tax payments on 110% of 2020 but did NOT include the amount he was entitled to defer as part of his tax even though he did not defer it.  So his payments were based on $8,537 less than the actual tax for 2020 x 110%.  IRS says he underpaid.  IRS FAQ #22 says

22. Is there a penalty for failure to make estimated tax payments for 50 percent of Social Security tax on net earnings from self-employment for the payroll tax deferral period?

No. For any taxable year that includes any part of the payroll tax deferral period, 50 percent of the Social Security tax imposed on net earnings from self-employment attributable to the payroll tax deferral is not used to calculate the installments of estimated tax due under section 6654 of the Internal Revenue Code. This means that self-employed individuals that defer payment of 50 percent of Social Security tax on their net earnings from self-employment attributable to the period beginning on March 27, 2020, and ending on December 31, 2020, may reduce their estimated tax payments by 50 percent of the Social Security tax due for that period.

Any idea who is correct on this?  IRS or Proseries?