So if mouse is a viewport that can’t be translated to a Vector2i without explict conversion. There are at least 8 potential Vector2 values that a Viewport contains, which one could you mean? Godot will not pick .get_mouse_position() for you out of the others, Godot doesn’t know what your intentions are.
Still, it would help to paste the _mouse definition. Seems like last time you had this line:
Which does end up a Vector2i. So what do you have now?