You should be able to just print it out and mail it now. Was it done or do you need to finish it?
How to Access prior year online returns
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-access-my-prior-year-return/00/27010
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 2024 for the side menu to open up. Just continue a little ways into 2024. I had to go though about 12 screens.
@travisbens be warned that if you are filing a 2021 tax return,
1) if you owe, you owe.
2) if you are due a refund, the window to claim that window closed on April 15, 2025 They IRS will not send you this money. However, if you applied for an extension back in early 2022, the window won't close until October 15, 2025.
Are you stating way back when you began the 2021 tax return using the online version and you never filed it. Yet you now want to finish this activity, but TT doesn't work on your personal computer? You have to PURCHASE the 2021 desktop version and load it onto your computer. It should work!
https://turbotax.intuit.com/personal-taxes/past-years-products/2021/
Can I ask why you are now just filing?
What is the problem with the desktop software not working on your computer? Is your computer too old--does it not meet the system requirements for the 2021 desktop download software? You can only use desktop download software on a full PC or Mac, not on a Chromebook or any other kind of mobile device. If your computer does not meet the system requirements, do you have a friend or family member who will allow you to download the software so you can complete the 2021 return?
As already explained above by VolvoGirl and NCperson, it is now too late for you to receive a refund for a 2021 return unless you requested an extension for 2021 before the filing deadline in 2022. Your refund has been forfeited. If you owe tax due, it is owed with late filing penalties and interest, for which the IRS will bill you after they receive the return and your payment of the amount due as shown on line 37 of the Form 1040. TurboTax will not calculate the interest or penalty.
Your 2021 return can only be filed by mail; it cannot be e-filed.
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.