To do a prior year return you have to buy the Desktop program here, they only sell ghe download, not the CD.
https://turbotax.intuit.com/personal-taxes/past-years-products/
You will need a full Windows or Mac to install it on.
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.
Then when you file for 2021 you need to enter 0 for the 2020 AGI since you are filing late.