Highrez

XMBC Version: 2.19.2
Windows Version: W10 21H2
Mouse Information (brand/model): Kensington 4-button
Relevant Computer Information (CPU, RAM etc): Ryzen 6core
How long have you used XMBC?: Newbie
What language and keyboard layout do you use in Windows?: En

Clear description of the problem - try and include as much information as possible, including what button and mappings you are having problems with (if applicable).: Trying to setup when I press the left and right buttons together, it acts like a middle click. Checked the manual, it didnt help. Assistance is appreciated.

OK, I think what you want is button chording.
Set this up on left AND on right button (because either could be the first button pressed I guess)
And in the chording configuration for left, set the right button to middle click, and the chording setup for the right, set the left button to middle click.