"Practitioners that have made a good-faith effort to meet the filing deadlines on behalf of their clients, but are unable to do so due to COVID-19, should write "COVID-19" in an attachment to the return briefly describing the reason they cannot meet the deadlines, or, if possible, should write "COVID-19" at the top of the tax return to indicate the need for penalty relief."

From these folks:

https://www.journalofaccountancy.com/news/2020/sep/coronavirus-pandemic-sept-15-filing-deadline-diff...

Not the IRS. The only reference I've seen points to this article as "evidence:"

https://www.irs.gov/businesses/small-businesses-self-employed/penalty-relief-due-to-reasonable-cause