For the life of me I couldn’t get my mouse to work when I had a mouse and keyboard on a single dongle. I ended up getting a mouse and keyboard that have their own dongles and the mouse still wouldn’t be recognised even though it showed in control settings. My workaround is that I unplug the keyboard dongle on start up and plug it in once i press the mouse button on the “Press any Button” screen. The keyboard dongle is plugged into a dongle extension so I don’t have to worry about wear and tear or damage to my Xbox USB Port. Works for me every time now so I’m happy with that.