Always use images with a square (1:1) aspect ratio on your product page. Never a portrait aspect ratio. Portraits pushes your key content (image gallery, variant picker, etc.) down the page. This doesn’t comply with Place the main image, thumbnails, and swatches in the same viewport
But, square images reduces vertical space and thus push your key content higher up the page. This also reduces friction for visitors going through your different product variants. With portraits, your visitors must scroll down to select another variant and back up to see the image. There's less scroll with square images.
The same holds for your collection pages.