Just in case this is of any use to anyone here, I mailed my 2020 tax year 1040 paperwork to the appropriate US office here (Kansas City, MO is the processing center for my state). I sent it certified on 11 February. It was finally delivered to the IRS on 23 February. As of today, 2 April, the IRS is acknowledging receipt under the "Where's My Refund" link on the IRS website. So, from the time it was delivered to the IRS until the time they logged it as arrived and in-process online was around five weeks. That's not bad at all, considering.
We had to re-send the daughter's 2019 1040 as it had been over a year since they should have processed it (it was in the same envelope as mine for that year, and mine was processed last June). Even the IRS agent on the phone admitted it probably had been lost. She recently sent the new copy of her 2019 1040 via Priority Mail to Austin, Texas (since she was living overseas in 2019). Priority Mail is billed as taking 2 to 3 days. It took about 10 days to get there, according to USPS tracking.
So in case you have to send your tax forms in hardcopy, be aware that there is still apparently still a delay in the USPS delivery systems. One of the couriers might be a better option. DEFINITELY send it tracked, whatever you do.
