Currently, with macOS Catalina 10.15.2, when you are swapping command and option keys in key preferences, they will not only swap command and option, but also left and right, thus the left cmd key will be mapped to the right option key. If you then use Fusion to map cmd to Alt and option to Ctrl, this swap also propagates. When your guest is running Windows, and you use a keyboard layout with AltGr this is quite annoying.
So for now, the easiest way to fix this is to use Sharpkeys ( https://github.com/randyrants/sharpkeys/releases ) to modify you registry to undo that swap. The attached file is a configuration for sharp keys swapping ctrl and alt-left /AltGr back.