Do you need to animate movement of the crop rectangle?
One way is to use Automatic video mode (or custom one that is 5.3K), make the project timeline, click Export > Video > Reframe. In the Reframe filter, change the size to 3840x2160. Then, drag the on-video rectangle control around to choose the area to include. Next, you can turn on keyframes and move the rectangle at different points in time. You can even track the motion of an object.