This is my favorite fidget, and I’ve found the most effective one for me. It’s a knot made of steel rings that slide over each other in endlessly entertaining ways. It’s extremely quiet and nonchalant–I’ve used it during lectures with no issue. It takes no actual attention to manipulate, which is what I love most about it. It takes up the distractible part of my brain and lets me focus on what’s important.

I got this one from https://www.etsy.com/listing/174256776/fidget-mobius-puzzle-chainmail, they also have lots of colors and different sizes.