When MeF is shut down on 11/18, you can't e-file any 1040, regardless of year, until it reopens at the end of January.

When the business system shuts down (towards the end of December), you won't be able to e-file any 1120 / 1120S / 1065 returns, regardless of year, until it reopens in early January.

Yes.... individual shut down is on 11.18.23, and includes ALL years.  AND that's the last day for efiling any 2020 returns.

Business is sometime in Dec (I'm not sure of that date).

Or are you referring to the IRS moratorium on processing ERTC claims until December 31?  Maybe the only way to find out is to try.  

No-   We have to file amended returns for the ERTC received for 2020 and 2021.   They already received the money.  Amendments are in process for the businesses and individuals that recieve a K-1.   Since the processing time for the IRS already is slow making them paper returns will make it even slower.

The processing time is the same for paper and electronic returns.  Mail delivery just delays the start by a few days.