I'm using my mouse left handed - primary button on the right of the mouse.
My Raspi is configured to use the mouse this way
My Win10 machine is configured to use the mouse like this.
But when I open RealVNC Viewer on my Win 10 machine, the mouse requires right handed use.
I can't find a setting in either the Raspi Server settings or the Win10 viewer settings to correct this.
PS: RealVNC - GREAT JOB!