Ya know patience is a virtue
I adopted a Maine Coon a few years ago and I have no idea what his previous owners did to him but he was a bundle of nerves. He couldn't relax and trying to pet him was almost impossible, 2 strokes and he'd try to bite. Plastic bags sent him running, he'd scream at my other cats and chase them.
Fast forward a few years and he's like a totally new cat, not that I'm saying it will take your kitten that long! It took patience and just letting him adjust at his own pace. Oh I just remembered something you can try is the slow eye blink. I've seen Jackson Galaxy do this and I've tried it on my own cats. It's just what it says, it's a slow blink while looking at your cat, seems to really calm them down and they'll return it