TurboTax closed the online editions for tax year 2023 after October 2024.
To complete and file a 2023 tax return using TurboTax you would need to purchase, download and install on a personal computer one of the 2023 desktop editions from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/
A 2023 tax return can only be printed and mailed, it cannot be e-filed using TurboTax.
Did you enter 2023 into the Online version? Online is only for 2024 now. Better try to clear it out so it doesn't accidentally get filed as a 2024 return and you can use it for your real 2024 return.
To do a prior year return you have to buy the Desktop program here,
https://turbotax.intuit.com/personal-taxes/past-years-products
You will need a full Windows or Mac to install it on.
Or how to finish a return you started online
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-started-in-turbotax-online/01/26322
If you want to file for free you can fill out the forms by hand. Here are some basic forms…..
Here is the IRS 2023 Form 1040
https://www.irs.gov/pub/irs-prior/f1040--2023.pdf
or if you want bigger type use 1040SR for Seniors,
https://www.irs.gov/pub/irs-prior/f1040s--2023.pdf
And 2023 Instructions
https://www.irs.gov/pub/irs-prior/i1040gi--2023.pdf
2023 Tax and EIC Tables
https://www.irs.gov/pub/irs-prior/i1040tt--2023.pdf
Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2023.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2023.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2023.pdf
Then when you do file 2024 enter 0 for the 2023 AGI since you are filing 2023 late.
You have to print and mail prior year returns. When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return. Don’t forget state.