The mouse-region widget does not correctly update the cursor, until the mouse is moved.

Here's a video showing the issue:
https://user-images.githubusercontent.com/736973/108889501-b1fdab00-75c9-11eb-9116-42023328fd29.mp4

The basic code example is that there is some overlay layer, inside a stack, that turns on to enable this cursor:

if (_isSpaceBarDown) ...{
                      MouseRegion(
                        cursor: SystemMouseCursors.move,
                        child: Container(color: Colors.transparent),
                      )
                    }

In this case _isSpaceBarDown is obtained using RawKeyboard.instance.addListener and a setState is called when it changes.