Did you use the Online browser program or the Desktop installed program? If you used the Online version you can download the pdf file. If you used the Desktop program you need the 2020 program installed to open it. Where did you buy the program originally? If you bought it from Turbo Tax you can download it again. Or ask support for the program.
OR you could try the TaxPrinter service to convert a .tax file to pdf at
https://www.taxprinter.com
They might be expensive and it is probably not safe to email tax returns back and forth. They are not related to Turbo Tax.
The 2020 tax data file with a file extension of .tax2020 can only be opened by the TurboTax 2020 software.
TurboTax does not have a process to produce a PDF from the tax data file.
The 2020 software can be purchased and downloaded from this TurboTax website - https://turbotax.intuit.com/personal-taxes/past-years-products/
However, there is a company that will do what you need for a price and is not associated with TurboTax or Intuit - https://www.taxprinter.com/