If you're viewing on mobile, I find it helps to tilt the screen away from you and look from below until it hits a sweet spot (or look from further away). It flattens a lot of the detail and brings out the contrast, so the magic eye-esque image comes to the fore.
Otherwise I've always been astigmatism gang pretending to see a palm tree on a page of technicolour squiggles after half an hour so the other kids don't laugh at them
No you're supposed to either cross your eyes or look through the picture for stereograms to work. And by look through the picture I mean focus your eyes so that you're not looking at the image, but past the image. The exact depth your eyes need to be focused on varies and it can take a while for your brain to parse what it's looking at but imo the animated ones are easier to see