2. Asking this question shows that you are still a beginner in CATIA, because beginners often encounter this problem. As long as the mouse clicks on the coordinate system in the lower right corner of the view, it will enter the model tree adjustment mode. In this mode, the model of the view will be grayed out and cannot be selected. When you roll the wheel, the model in the view will not be enlarged, but the model tree on the left side of the view will be enlarged. You can exit this mode by clicking the coordinate system in the lower right corner again.

3. This mode is set for the convenience of adjusting the model tree during modeling. Because when the model is complex, the history of the model tree will be very long, and dragging the model tree will be more troublesome.