According to another Intuit Accountants site, located at:
https://proconnect.intuit.com/community/individual/help/2019-e-file-start-and-stop-dates-for-federal....
IRS Annual maintenance and e-file closures
The IRS normally shuts down their e-file servers in November and December to prepare for the upcoming tax year. The Intuit Electronic Filing Center will stop accepting e-file transmissions before the IRS shutdown to ensure that all e-file submissions are received by the IRS before the shutdown.
After the shutdown, you'll no longer be able to e-file tax year 2018 returns nor receive e-file acknowledgements for tax year 2018 or prior returns. Tax year 2019 and 2020 returns can still be e-filed when the IRS re-opens for the tax year 2021 filing season.
