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:
 Open the Xencelabs Driver, then click on the 3-Button Pen or [Thin Pen] option on the left.
 If you have added Adobe PS to the application row, please select Adobe PS first in the application row.
 Choose one of the buttons to set up, for example [Middle Button].
 Clicked on the [Middle Button] option.
 Scrolling down to [Modifier…] and click on it.
 Check [Control+Option+Left Click].
 Click on [OK] to save the settings.
Then open Photoshop and test, it should work.