Magic Mouse works apart from scrolling (USB-C connector)

Old Magic Mouse with Lightening connector works as spec including scrolling.  Messages displayed when connected or disconnected.

New Magic Mouse with USB-C connector works apart from scrolling.  No messages displayed on connecting or disconnecting.

Both mice work as above when connected one at a time or both together.

Restarting computer in normal or safe mode, with and without blue tooth active, makes no difference.

Apple MacBookPro 13” M1 2020.  Using external drives and Apple Studio Display but above things apply with or without them.