When I add a camera it is really tiny, hardly visible. So I scaled it up. But when I "Align Camera to View", the camera is scaled back to being really tiny again. You can see the same thing happening in the tutorial video, except that it is the opposite problem: Jonathan scales down the camera, and after Align Camera to View, it is large again.
I tried to apply the scale to the camera, but nothing happens: I scale it up to 100, select Apply Scale, but it stays at 100.
When you are on the camera, there is a setting in the camera menu (on the right, green camera icon)
There is a sub-item "Viewport Display". If you set the size there, it will not change when you use "Align Camera View".