Custom icon for shortcuts are warped/squeezed/stretched.

I am making shortcuts with custom icons for my homescreen on my iPad. It doesn’t matter what size the square image is… 67x67, 512x512, etc… the images are being warped by the shortcuts app and being squeezed into a rectangular shape. It’s not super apparent until you have an image that contains a perfect circle, then it’s unmistakeable, because the circle becomes an oval.

So, since the internet tells me to use a square canvas, I’m here to ask if this is not actually appropriate. Is there an ideal rectangular canvas size that I should use to make custom icons?