Dust can come in many forms, first of all, it can install itself in your camera due to static this is a pain in the butt, I know I’ve been In this situation but it could also come from the fastest of lens changes nothing you can do about this sometimes.  but not all is lost although you can’t see the dust with your Naked eye it’s for sure on the sensor don’t forget when you see a spot on images its zoomed around 400x in some instances to show the dot on your work. Photoshop does well to remove them if you have one or 2 any more than maybe 5 id get the thing cleaned out..