The InputActions assets in the new input system are meant to create an abstraction layer between different pieces of input hardware and what actions their inputs are supposed to trigger in the context of the game.
That means Actions are meant to be semantic, not technical. You don't want to do something when the player clicked the mouse button. ...
You have to compute the angle of the vector from the player to the mouse. get the mouse position by pygame.mouse.get_pos() and the rectangle (pygame.Rect) around the player (self.rect ):
mx, my = pygame.mouse.get_pos()
player_rect = self.rect
Calculate the vector from the player to the mouse and compute the angle of vector by math.atan2. The y-axis needs ...