In the Mac system, If you are trying to set up the pen button with the shortcut Control+Option+Left Click to adjust the brush size in photoshop, but it doesn't work. Please follow the detailed instructions as below:

 

First, please install the Xencelabs Driver.

Driver version: XencelabsMac_1.1.0-8 or later.

Driver download link:

https://www.xencelabs.com/support/download-drivers


[1] Open the Xencelabs Driver, then click on the 3-Button Pen or [Thin Pen] option on the left.


[2] If you have added Adobe PS to the application row, please select Adobe PS first in the application row.


[3] Choose one of the buttons to set up, for example [Middle Button].



[1] Clicked on the [Middle Button] option.

[2] Scrolling down to [Modifier…] and click on it.

[1] Check [Control+Option+Left Click].

 

[2] Click on [OK] to save the settings.

 

Then open Photoshop and test, it should work.