I’d be willing to bet some form of shift/ctrl/alt + right/left click exists in at least 95% of the computer games (which use keyboard & mouse) created in the past decade.
I’ve played my fair share of ARPGs and I did not figure this out. I am aware of the ctr/shift + left/right click combo. Generally you can add/buy stuff in bulk with it but not in this game, so I gave up on it. To me, this is all not very intuitive. Maybe a tutorial tip would help.