I use the Polar Pro ND and ND+P filters. They screw onto the camera threads, so I have to remove the stock lens cover to put them on.
The stock DJI P3-045 is a mild polarizing filter. I would think you wouldn't want to stack filters like that in most situations. At least on my regular Nikon, multiple filters can create unexpected light refractions and reflections so I keep to one filter at a time to control the effect.