So, the first half of the video is testing the left-click move/attack functionality. I’ve set my left click to my right-click skill (Firebrand). I could not get this to work at all. I tested all my other active abilities, as well, and they did not work either.
The second half shows what @Folks mentioned earlier. You can get the shift attack function to keep you in place until you combine any movement with said function.
Hopefully this helps!
Yeah… I’m an old man and set in my ways, I really don’t have the mental dexterity to figure out how to play without shift-makes-you-stand-still-while-attacking. It’s how I play other games like this, I keep waiting for this to get settled so I can really dig my teeth into Last Epoch. Ahh well.
Happy to note… just jumped into the game to see the state of play…
SHIFT HOLDS ME IN PLACE SO I CAN ATTACK WITHOUT MOVING!
Sooooo time to play. 
Next question - can you rebind Shift to another key like space bar?
No idea, I haven’t tried yet. I figured I wouldn’t look a gift horse in the mouth and jinx it.