The IRS e-file Signature Authorization form is Form 8879. That form is never used when you file your tax return yourself with TurboTax. Form 8879 is used only to authorize a paid tax preparer to e-file your tax return for you. You don't have to authorize yourself to file your own tax return. Form 8879 is not included in TurboTax because it is never used when you file with TurboTax.
If someone is asking you for an e-file Signature Authorization for your tax return, either they think you paid someone to do your tax return, or they don't understand how tax returns are filed.
You can download a blank Form 8879 IRS e-file Signature Authorization from the IRS web site.
If you efiled there should be an Electronic Postmark page. Probably near the end. That is your proof and signature. If you print out your return to give someone you will have to sign it in ink now.
How to get or print a copy after filing
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-get-a-copy-of-a-return-i-filed-this-year-in-turbotax-online/01/25932
The IRS e-file Signature Authorization form is Form 8879. That form is never used when you file your tax return yourself with TurboTax. Form 8879 is used only to authorize a paid tax preparer to e-file your tax return for you. You don't have to authorize yourself to file your own tax return. Form 8879 is not included in TurboTax because it is never used when you file with TurboTax.
If someone is asking you for an e-file Signature Authorization for your tax return, either they think you paid someone to do your tax return, or they don't understand how tax returns are filed.
You can download a blank Form 8879 IRS e-file Signature Authorization from the IRS web site.