Do you need to file a 2023 return for him? You can't use Online to file 2023. Online is only good for 2024. Will you also need to file an Estate return? That is separate.
To file a personal 2023 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.
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 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
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.
