For the universal updater go here:

https://support.8bitdo.com/firmware-updater.html

If your controller is not detected, you might be on an older FW version that is not detectable by the universal updater. How do I know this? Because my SN30 Pro SN Edition wasn’t detected for this exact reason.

If this is the case, go here to access legacy firmware:

https://download.8bitdo.com/Firmware/Controller/

Update your controller to the latest version for your device, and then try the universal updater again.

Also, make sure your controller is in update mode. For the SN30Pro you do this by pressing L+R+START and the red light on top starts flashing. It might be different for other controllers though.

Hopefully this helps someone. It took me quite some time to find the legacy firmware installers to fix my controller.