I run Dragon on my Parallels. Calling Dragon's tech support, I was asked to run About Dragon to see my serial number. I do, but the window is so tiny that the serial number is illegible - even with a magnifying glass! Resizing the Parallels window works for a second - then the Dragon window resizes itself small again. I go to Windows settings > Display. "A custom scale factor is set". Even if I "turn it off and sign out", it's back when I sign in, Parallels is overriding this. Can't find a relevant setting in Parallels. How can I manage this?
Found it. "Windows 10" menu bar > View > Retina resolution > Best for external displays. Gives you back control over each display's resolution. 200% worked well for me.