Joanne -

Did you go here? https://www.irs.gov/newsroom/filing-and-payment-deadlines-questions-and-answers

If you look at the 7th question under eligibility it is:

"Are the filing deadlines for partnerships and S-corporations whose returns were due to be filed on March 16, 2020, postponed?

I would say that does directly answer your question.

As far as Notice 2020-23, in my opinion (for what it's worth!) the operative language is found in the first sentence under III. GRANT OF RELIEF A. Taxpayers Affected...….

"a Federal tax return or other form filing obligation specified in this section III.A (Specified Form), which is due to be performed (originally or pursuant to a valid extension) on or after April 1, 2020, and before July 15, 2020"