The USB dongle is plugged in. Does this override Bluetooth settings in options? If yes, is it possible to truly turn off Bluetooth connectivity and how would you test that, since the Bluetooth setting itself is toggled off? If not, how is it doing this?
Trying to search for the answer via search engine just gives me troubleshooting to make the mouse connect, which is the opposite of my question.
This is most likely. I have a wireless mouse which has an option to switch between direct 2.4GHz connection to a dongle and Bluetooth. I use the latter when on my laptop, but the former when on desktop PC.