How can I get my player to be able to attack while running?

just add an inverted is Attacking to the player run animation action.

It currently sets the animation to run every tick while the player is moving, instantly overwritting the attack animation.

tbh I'm a bit confused how or why your character and animation controller is setup like it is.

looks super neat though with the nice sprite and 3d camera movement

What confused me is that you didn't use animation triggers but instead set the animations every tick while something is true.

Aswell as the stacked else conditions, makes it a bit hard to read. I would probably use inverted conditions instead.