Online is only good for 2024 now. Sorry it's too,late to start a 2023 or prior online return or use the mobile app, either on Turbo Tax or the IRS. And too late to efile 2023.
If you need to start 2023 or prior you can buy the Desktop download here,
TurboTax 2022 Prior Year Tax Prep - File Past Years' Taxes
You will need a full Windows or Mac to install it on.
If you have a simple return and want to file for free you can fill out the forms by hand. Here are some basic forms.....
Here is the 2023 1040 return
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
2023 1040 Instructions
https://www.irs.gov/pub/irs-prior/i1040gi--2023.pdf
2023 EIC and Tax Tables
https://www.irs.gov/pub/irs-prior/i1040tt--2023.pdf
Schedules 1-3
https://www.irs.gov/pub/irs-prior/f1040s1--2023.pdf
https://www.irs.gov/pub/irs-prior/f1040s2--2023.pdf
https://www.irs.gov/pub/irs-prior/f1040s3--2023.pdf
Don’t forget your state. And you will have to print and mail your returns. So be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.
Did you already start a 2023 return before Oct 15? 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 can't get the side menus to open up to access the prior year..... You need to start entering some basic Personal Info in 2023 for the side menu to open up. Just continue a little ways into 2023.
Then when you do file 2024 enter 0 for the 2023 AGI since you are filing 2023 late.