This function is only available in manual focus mode and is activated by double-tapping the subject in focus. This function is designed to bring the subject into focus instantly by magnifying the viewfinder image four times (2x zoom). The image quality of the zoomed-in part of the viewfinder depends on the resolution of the viewfinder. If you want higher quality, you have the option of using the appropriate viewfinder resolution setting.
The function keeps track of where you double tap. And it zooms in exactly to that location. For this reason, viewfinder magnification was chosen to implement this function, rather than the quality zoom on the sensor. Zooming in on the sensor on most devices is only possible in the middle, and does not give the advantage of zooming in to any point on the viewfinder image.
When this function is activated, the stroke of the manual focus ring is doubled, i.e., the orange working area becomes twice as large. In this state, the black focus position indicator may extend beyond the screen.
This function may conflict with the setting of hiding individual interface blocks, because hiding interface blocks is done by touching.