Hey again, Ranma.
I don’t know if I had anxiety or anything else when I was that young (apart from ADHD, obviously), but I spent a lot of time chewing the inside of my mouth. I still do it from time to time. Never enough to damage, but always enough to hurt a little.
There’s a chance that a fidget toy of some kind could help you with that. I’d maybe tentatively recommend a fidget cube, or a fidget pen. Several of them are designed to be noiseless.
Hope this helps 🙂