As already mentioned in the purchase criteria, retrofitting the drone with camera is only possible for flying objects with indirect integration of the camera. You should pay attention to the weight and therefore the carrying capacity of your drone type. This is the only way to be sure whether it is possible to exchange it for a heavy camera, for example. The rule here is as follows: the larger the drone, the greater its ability to carry a heavier load.
Most product types also come with a camera kit, which makes replacement much easier. However, cheaper models may have camera mounts that are not interchangeable. The costs are much higher, so you should already be clear when buying your drone whether you ever want to upgrade it.