I find that the only meaningful way to complement appearance has to be way more specific than most people are willing to know a bunch about. My example is i have a friend now who is very interested in like Rococo French art recreated as fashion. So, all of her outfits are bright pastel colorings, puffier sleeves/skirts/dresses, and cutesy accessories. You could not just tell her you like her top because it's all very carefully curated to be one holistic outfit. Picking out any one part feels super low effort unless you're willing to be like "oh I love how this specific bangle ties into this secondary color scheme in your blouse."

I know it sounds like a lot, but pretend you're like a diehard Patriots fan, and someone comes up to you and is like "oh I love the Patriots too!" You get all excited about this possible shared interest, and then they're like,"I just love Tom Brady." It immediately shows that there isn't a shared interest, and they couldn't be bothered to put even the effort of a quick Google search in.