Tried to e-file and got the following message: Your transmission didn't go through Tax Year 2021 transmissions are not available.

[mesquitebean]

It could be due to some form not yet being available for efiling.  Here's one possibility:

Do you have a state return, and does it happen to be North Carolina by any chance?

If so, some NC forms (including the main Form D-400) are not yet finalized and available for efiling.   Projected availability date is 2/24/2022, according to the availability tables:

State Forms Availability Table:
https://ttlc.intuit.com/community/forms/help/state-forms-availability-table-for-turbotax-individual-...

If that's your situation, and if you wish, you can efile the Federal return now (if all your Fed forms are available) and efile the state return later.  To do that, you would need to temporarily change the filing method for the state return and tell TurboTax that you intend to "mail" the state return.  Then when the state forms are available you can switch the method back to efile.

If you need to check on Federal forms:

TurboTax IRS Federal Forms Availability Table:
https://ttlc.intuit.com/community/forms/help/irs-forms-availability-table-for-turbotax-individual-pe...