He then plugged in a standard USB mouse, confirming that these can also be used with Switch 2 hardware. When the mouse is plugged in, a message on the screen shows that the mouse is connected and takes priority over the Joy-Con 2’s mouse controls.
Ryu then showed that it was possible to use the USB mouse with the right hand, but continue to use the left Joy-Con 2 with the left hand, meaning all the controller shortcuts are still available even when using a standard mouse.
This was actually my assumption for the mouse controller Nintendo showed.
The real feature is full pointer support! The built in mouse is a gimmick to introduce full pointer support.