Why is my screen resolution 810 x 1080?
For some strange reason this website is showing iPad screen resolution as 810 x 1080
Note this is the iPad 9 generation
Perhaps an illustration will help.
Here is a non-Retina screen compared to a Retina screen. This picture is from 12 years ago, BTW.
The images on the two screens are identically sized.
However, the image on the left is non-Retina, at 1 pixel = 1 display point.
The image on the right is Retina, with 2 horizontal pixels and 2 vertical pixels per display point, for a total of 4 pixels per display point. People call this 2X scaled, but it's actually 2x2 scaling, for 4 times the pixels.
Your screen has 1080x810 display points, for a total of 874800 display points.
However, your screen has 2160x1620 actual pixels, for a total of 3499200 pixels.
874800 display points x 4 pixels per display point = 3499200 pixels.
You could theoretically make a Retina screen 1:1 pixels to points, but then everything would be too small and impossible to read. Apple has specifically designed the Retina screens to be 4:1 pixels to points.