If you use TurboTax online, the filing fees include both preparation and e-filing. There is no extra charge for e-filing and there is no discount if you don’t e-file. You are mainly paying for the preparation service, and if you print your tax return and mail it in, you have still received the preparation service.
If you use the TurboTax desktop version installed on your own computer from a CD or download, the federal program includes free e-filing and there is no discount if you don’t e-file. You still receive a prepared tax return that you can mail. There is an extra charge to e-file your state tax return when using the desktop program. If you paid that fee and were unable to e-file, you can call customer service to get a refund.
I don't know if you can efile a return with the injured spouse form but this FAQ says if you efiled your return you can mail the 8379.
FAQ Injured Spouse Form 8379
This Forms Availability list says 8379 is available to efile. If your return rejected it might be for something else.
https://care-cdn.prodsupportsite.a.intuit.com/forms-availability/turbotax_fed_online_individual.html
Form 8379, Injured Spouse Claim and Allocation is available for e-filing with the federal tax return for tax year 2020.
See - https://care-cdn.prodsupportsite.a.intuit.com/forms-availability/turbotax_fed_online_individual.html