Using latest official release 3.6.2. I can select my camera in the sidebar in View > Local Camera and in the Scene menu, but the Camera object is not listed in the Outliner nor is it visible in the 3D Viewport. Is this a bug or is there a view option I'm not aware of?
Blender keeps information of an object which has been deleted. It deletes the object but keeps the information about it.
For example say you had 2 cameras in your scene. Cam A and Cam B. Now you deleted cam A. Then you decide to add another camera called Cam C. The only property you had changed about these cameras were their focal lengths. A had 35mm. B had 50mm. And C has 85mm. Now if you go to the object data properties of Cam C. You will see a drop-down menu on the top. The name of the object will be Cam C. But the name you will see in that menu will probably be camera.002. Now if you open that menu you will also see camera and camera.001. These are A and B. Now the fun part. If you choose camera from this list. You will actually bring back the information about camera A, and replace the information of C with A.
You can even have two objects sharing the same data. Like both B and C can share info from B. In fact when you duplicate objects using Alt+d you don't actually create an instance of the object. You create something called a linked duplicate. That is nothing but another object sharing the same data as the other object. You can have every single object sharing the same data! (Obviously only as long as they are the same data type)
Now back to the example. If you delete Cam A, close blender, reopen it, and now of you try to replace C's data with A's, it won't be there. Once you delete an object blender stores it data until you close the file.
So now to your actual case. There is no camera in your scene. But there is a camera in that list. Well, you must have deleted the camera at some point. Now the data is still there, but the object isn't. So you will see the camera in that list, but it won't be actually there in your scene.
If that's not the case, well, the only thing that I can think of is that you marked the camera data as a fake user. You can do that by clicking the shield icon next to the name in the object data properties. What it does is, that it just saves that data in a way, such that, if you delete the object with that data and close blender, the data won't be deleted.