Fundamental changes
The first thing you notice in the new UI is the complete separation of photo and video modes.
Another major difference that you might not immediately notice, but will definitely feel if you are used to the current camera experience on Pixels is that Google has swapped the location of the camera switch button with the gallery preview button.
New (old) modes
Another part of the layout refresh is the reshuffling of some established modes, most likely to make features more prominent for users who might not have known they existed.
The “Motion” tab has been split into “Long Exposure” and “Action Pan.” The modes themselves are not new, but they each now have a separate tab to increase their visibility.