Reconfigured Mouse Buttons Don't Work With Keyboard Modifiers

If I reassign a mouse button to a keyboard button, I can't use that click with a modifier.

For example: I reassign Mouse Button 3 to "Left".
When I hold Shift on my keyboard and click Mouse Button 3, I expect macOS to register Shift+Left, but it doesn't.

I'm using an Evoluent VM 4 on a Macbook Pro 2017 running Big Sur 11.6.1 and BetterTouch 4.034.