I'm not sure if this is exactly what you want, but you can rotate the camera towards the mouse pointer like this:
extends Camera2D
var center
func _ready():
center = get_viewport_rect().size * 0.5
set_process(true)
set_rotating(true)
make_current()
func _process(delta):
var mouse_pos = get_viewport().get_mouse_pos()
set_rot(-center.angle_to_point(mouse_pos))