Image renderer stretching sliced images

I use an Image component which stretches a 9-sliced sprite.

Vertical squishing occurs when the image’s RectTransform height is less than half of the sprite height. Your sprite is very large, 2048×2048 for a very low-detail image. You could probably get away with a 64×64 or even a 32×32 sprite. Just check the image’s RectTransform height in the Inspector and make your sprite double that number. Remember Unity likes sprites with a width and height that are a power of 2: 8, 16, 32, 64, etc.