The original Mavic pro camera (FC220) could be user replaced if the unit needed replacing due to failure or damage.
The Mavic 2 drones (when first released) could have their cameras swapped if the user fancied turning the Zoom variant into a Pro: interchangeable 'payloads' - very similar to what was possible with the Autel Evo 2 airframe.
DJI worked out pretty quickly that they could make a bit more money out of Mavic 2 owners if they locked one camera with one airframe - that way, the only way to replace or change the camera was to send the whole drone in to DJI and pay them the £350+ fee.
Since the firmware introduction of serial number pairing between the drone and the camera unit it has become very very difficult to self-repair, replace, or swap camera units.