Can someone please explain the purpose and function of the yellow rectangle around the camera? It seems to have a mind of its own. I'm also having trouble keyframing camera movement and am not sure if it's related.
It is part of the new gizmo system.
Certain object types have a new gizmo that allows controlling specific object properties directly from the 3D view.
For cameras you can control the focal length.
For spot lamps you can control direction and angle.
Other object types have different controls.