Can I file my 2021 taxes in 2024?

For your personal return or a Business return?                        

Sorry, Online is only for 2023 now. Online for 2022 and prior is closed now so you can not start a new 2021 or prior return or finish one. You have to do each year separately

How to prepare a prior year return
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-prepare-a-prior-year-tax-return/00/25984

To do a prior year return you have to buy the personal or Business Desktop programs here,
https://turbotax.intuit.com/personal-taxes/past-years-products
You will need a full Windows or Mac to install it on.

If you want to file for free you can fill out the forms by hand. Here are some basic forms…..

Here is the IRS 2021 Form 1040
https://www.irs.gov/pub/irs-prior/f1040--2021.pdf

or if you want bigger type use 1040SR for Seniors,
https://www.irs.gov/pub/irs-prior/f1040s--2021.pdf

And 2021 Instructions
https://www.irs.gov/pub/irs-prior/i1040gi--2021.pdf

2021 Tax and EIC Tables
https://www.irs.gov/pub/irs-prior/i1040tt--2021.pdf

Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2021.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2021.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2021.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.