This is a developing issue this morning. Several other desktop users have reported the same, and they were able to proceed to efile anyway.
Obviously that message has an error since October 17 is the extended filing deadline this year for the 2021 return.
2021 Dates and Deadlines:
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-calendars/tax-year-2021-calendar-imp...
Did you get a confirmatory email that the efile had been transmitted, and when you check the efile status from within your desktop software, does it show you the efile status?
I bet there will be a lot of other users encountering this message today and posting about this in coming hours. Hopefully, there will be word from TurboTax folks at some point.
Also, be aware that if an efiled return is rejected after it was timely efiled on or before October 17, one has until October 22 to make any corrections and either resubmit the efile or postmark and mail the rejected return.
