Windows 10 Pro doesn't show version of Windows, can this be fixed?

The simplest way is

• Click Start
• Type winver
• Hit Enter.

This works at least back to Windows 7, if not earlier [nothing to test that on]

Go to Start, System, then About (scroll down to the bottom of the left side list to see About) and that will tell you the Version (say 1909) and the Build (18363.393).

Unless you have a Long Term Service version (Companies can do this), Windows 10 will inevitably update, so you need to contact the vendor of the paid software to let them know Windows 10 changes feature versions every 6 to 9 months.