Is there a way I can file back taxes from 2020 with turbotax?

Sorry you can no longer use Turbo Tax to prepare or amend a 2020 return.   Not Online and not using the Desktop program.  You need to do it yourself or go to a local tax place or accountant.

Even if you find or reinstall the Desktop program,  you will never be able to activate the 2020 program with the License Code.   The License Code started in 2019.  So it needs to connect to Turbo Tax to verify the License Code.  But they have stopped supporting 2020 and prior.

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 2020 1040 return

https://www.irs.gov/pub/irs-prior/f1040--2020.pdf

or if you want bigger type use 1040SR for Seniors,

https://www.irs.gov/pub/irs-prior/f1040s--2020.pdf

2020 1040 Instructions

https://www.irs.gov/pub/irs-prior/i1040gi--2020.pdf

2020 EIC and Tax Tables

https://www.irs.gov/pub/irs-prior/i1040tt--2020.pdf

Schedules 1-3

https://www.irs.gov/pub/irs-prior/f1040s1--2020.pdf

https://www.irs.gov/pub/irs-prior/f1040s2--2020.pdf

https://www.irs.gov/pub/irs-prior/f1040s3--2020.pdf

Don’t forget your state.  And you will have to print and mail your returns.  So be sure to attach copies of your W2s and any 1099s that have withholding on them.  You have to mail federal and state in separate envelopes because they go to different places.  Get a tracking number from the post office when you mail them for proof of filing.

It is too late to file to get a refund for 2020.  But you still have to file and pay any tax due.  If you do have a tax due the interest has been adding up so file as soon as possible.  

I have the TurboTax 2020 Business installed. I forgot and apparently did not download the State version in 2020. Is there a way to still download the state and install it into my 2020 TurboTax Business?