Ay, I am facing the same problems. But funnily, I tried to post my design on Instagram. At first, I thought JPEG was causing artifacts because I looked at the original export; it does have artifacts. So I change to PNG. Great, no problem, no artifacts shown. But when I upload it, boom, artifacts.
I’m curious. This is my first two weeks designing using Figma for my Instagram business account. Usually, I use Adobe Illustrator.
Instagram, like any other social platform, compresses images and stores them as jpg. And this seems to be completely unrelated to the Unity problem in the original topic.