Received a snail mail response on 2/5/21, the first time I heard from them.
"We received your reply on Nov. 20, 2020 to our notice about proposed changes to some of the items on your tax return. Before we resolve this matter, we need to process all of your information. We'll send you our complete response within 90 days. If you think you might owe any additional tax, you should consider paying it now. The law requires us to charge interest on unpaid tax from the due date of the return (not including any extension of time to file the return) to the date you pay the tax in full. If you have questions about this matter, you can call office of [some real person's name] at [phone number] between 7:00 AM and 8:00 PM MST". If you prefer, you can write to us at the address at the top of the first page of this letter. [Blah blah blah] Thank you for your cooperation"
Emphasis added by Progree
((Prior: 11/12/20 - received IRS Notice CP2000 11/12/20 dated 11/9 for 2018 Taxes that I owe $2,923. They claim I didn't report my BDA IRA RMDs but I did. -- I mailed my full blown response with many pages from my return and TurboTax "keep for your record" pages too on November 16. Given that they said they received it on November 20, at least my letter got delivered in a timely way ))