TurboTax for 2020 is no longer supported. You will not be able to get it to work. It's probably telling you there are no updates because the updates for 2020 are no longer available online. TurboTax supports only the current year and three previous years. Right now that means 2021 through 2024.
You could try using TaxPrinter to get a PDF of the tax return that's in the .tax2020 file. You send them your .tax2020 file and they send you back a PDF of the tax return. TaxPrinter has no connection with TurboTax. I have never used TaxPrinter, so I cannot make a recommendation. I'm just making you aware of it.
