When trying to access and print a tax return from the year 2020, the only available option is to download the return as a .tax file. How do I access this file as a PDF?

You will have to contact TurboTax support for assistance with this problem. 

See this TurboTax support FAQ for contacting support - https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/turbotax-phone-number/L0Od33nMQ_US_en_US?uid=lfgviwbm

Support can also be reached by messaging them on these pages https://www.facebook.com/turbotax/ and https://twitter.com/TeamTurboTax