If you started a 2020 online return, you should still be able to preview it or pick up the interview where you left off if you want to continue it.
When you log in, you should arrive at a page that asks you where you want to go (what topic) in the interview to continue it, or "pick up where I left off." If it instead has no evidence of your 2020 return and acts like it wants you to start a new return, then you likely have multiple accounts and signed into the wrong one. Many people end up with multiple accounts without realizing it.
You can have up to 5 accounts that use the same email address for notification purposes. A User ID may be an email address, but it doesn't have to be. It might be only part of an email address, or it can be anything at all.
To get a list of your User IDs, reset password, and recover account access, etc., you can use the tool at the link below. When using the Account Recovery tool, try using your phone number first if you can still access it. After that, if necessary, then run the tool on your email address(es) you can access.
NOTE: Before running the account recovery tool below, log out of all Intuit accounts including this user forum, or you might end up in a loop. Then clear your browser Internet cache, close your browser, then reopen it, and go to the link below. You may wish to copy this link so you can paste it into the new browser session.
If still no luck after running that on your phone number you can still access and email address(es) that you can access, here's another method:
Go back to the tool again, but this time leave the data field blank, scroll down a bit, then choose the small blue link that says "Try something else", and it will look you up by SSN and other parameters.
Oh, one other thing. We don't know exactly what you saw when you logged in. You didn't say how far you actually got in the interview when you were inputting information previously. If you actually finished the interview (or if TurboTax thinks you did), then your return interview may be closed. In that case, when you log in, it won't ask you to pick up the interview; instead the Tax Home page will have a return status. If that's your situation, we can tell you how to download/print a PDF of the unfinished return, or how to open the interview back up.
Again, if there is no evidence at all of a 2020 return in that account, and it's acting like it wants you to start one, then look for multiple accounts as I detailed in my first answer above.