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 2021 for the side menu to open up. Just continue a little ways into 2021.
If you used the Desktop CD/Download program then the only copy is on your computer and not saved or stored online. So you need to make and keep your own backups.
Or request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript
My guess here (based on no facts really) is that you e-filed your 2020 taxes using the online version of the program, with a different account from the one you are using to check this with. Check the e-mail address on the confirmation e-mails, and confirm you are using the correct account. Note that you can have up to 5 accounts with TurboTax under the same e-mail address.