I would like to save all 2021 tax data files (not just the return). I've downloaded the .tax file, but it wants an app to open. I only have the ONLINE Turbo Tax

[CarissaM]

It would be best to save the additional tax data files to your computer/device, as it will save the return as is. Saving the additional forms separately will ensure they are saved for future use. 

Also, what app is it prompting you to have?

[VolvoGirl]

Yes if you download the .tax2021 file you need the Desktop program installed to open it.   You should also download the pdf file with all the worksheets.

If you call in they might give you the Desktop program if you paid for the online version.

How to contact Turbo Tax
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-contact-turbotax/00/26991

What is the Turbo Tax phone number
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632