As Dougie states page 108 of the new camera book states
The first thing to note about the Raspberry Pi HQ Camera and Camera Module is that they both feature a rolling shutter. So, when capturing an image, the camera reads out the pixels from the sensor one row at a time. Unlike the global shutter on a DSLR
camera, it also lacks a physical shutter that covers the sensor when not in use.
Also note:
In addition, the HQ Camera or Camera Module acts more like a video camera than a
stills camera, as it is rarely idle. Once initialised, it is constantly streaming rows of frames down the ribbon cable to Raspberry Pi for processing.
...
For more details on how the camera hardware works, see the picamera documentation at magpi.cc/cameradoc.