You don’t need two copies of TurboTax. When TurboTax is installed on your own computer (the desktop version), you can prepare as many different returns as you want. Each return is a separate document, similar to a spreadsheet or word processing document. If you launch the program and go to the file menu you should be able to see the button to click for a new file, just like any other program that handles multiple documents.
Your tax return is probably stored in the main documents folder for your user account on your Mac or PC, with a name something like “John Smith 2019.tax2019”. (The “. tax2019” extension may not be visible depending on your system settings.) You can put your tax document anywhere you like, and you can have different tax documents stored in different places. The TurboTax application itself can only be installed on the same drive as you’re currently active operating system, and you can only have one instance of TurboTax for a particular tax year installed at any one time.
