Reading what mayflash has on their site, the purple LED mode is NOT for use on a PC. All it does is make the controller seem like a pro controller on the switch so it can support rumble. If you are using a PC, use only the blue or green LED modes (blue preferably).
--------------------- MERGED ---------------------------
Also, if you want to use a pro controller on the PC, you don't even need this adapter. All you have to do is connect it with Bluetooth. It works perfectly with my joycons, and I believe it also applies to the pro.