Tax Year Prior to 2020: I started an S corp in 2016 that did not generate any income or expenses.

Here is a link to the instructions for Form 1120S.

Who must file begins on page 2.

Interest and Penalties begins on page 4.

I did not read it in detail, but in a very brief glance, I didn't see anything that relieves the filing requirement for no current income/expenses.  Only if corporation terminated or the S election terminated, and even then, a final return appears to be required.

https://www.irs.gov/pub/irs-pdf/i1120s.pdf

@ " Started S corp in 2016 that did not generate generate any income or expenses" 

It doesn't really matter whether the S corp generates any income or expenses, you have an obligation to file a tax return for the S corp every year.

There are penalties levied at each shareholder of an S corp that can run well into a thousand dollars each for failure to file an S corp return.