Views in Zoom
There are 3 video layouts in Zoom when no one in the meeting is screen sharing: Gallery Mini and Active Speaker:
When someone is screen sharing, you can use Side-by-Side Mode or view the screen share with Active Speaker or Gallery View.
The Zoom Resource 'How Do I Change The Video Layout?' has an overview of each option.
Active speaker is the default layout, this layout will switch the large video window between who is speaking: