How do I prepare my 2021 taxes on Turbotax?

Online is closed for the 2021 tax year.

For the 2021 tax year you will have to use a desktop (installed in a computer) TurboTax version, which is not free.

See https://turbotax.intuit.com/personal-taxes/past-years-products/2021

No, you cannot prepare a past year return for free using TurboTax.  Only a 2023 return can be prepared using online TurboTax.  Past years must be prepared using purchased software that can be used on a full PC or Mac.

You cannot change the tax year.   The current online program is for 2023 only.   Only a 2023 return can be prepared online and only a 2023 return can be e-filed.

Online preparation and e-filing for 2020, 2021, and  2022 is permanently closed.

To file a return for a prior tax year

 If you need to prepare a return for 2020, 2021, or 2022  you can purchase and download desktop software to do it, then print, sign,  and mail the return(s)

https://turbotax.intuit.com/personal-taxes/past-years-products/

You may also want to explore purchasing the software from various retailers such as Amazon, Costco, Best Buy, Walmart, Sam’s, etc.

Remember to prepare your state return as well—if you live in a state that has a state income tax.

https://ttlc.intuit.com/community/state-taxes/help/how-do-i-contact-my-state-department-of-revenue/00/25573 

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/state received the return.

Federal and state returns must be in separate envelopes and they are mailed to different addresses.  Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.