Hello @235usr59tentwozero
welcome to this Apple (user-to-user) Community!
Re: "AssistiveTouch menu flashes bright then dims"
"I’m curios what is going on to cause the menu to brighten than dim."
Am no expert in this area, yet your post to us deserves some response.
No one in the community has offered an explanation, and two weeks have gone by.
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Re: "Most times it’s idle and not doing anything".
Seems the brighten- dimming is independent of anything you do, or any action you take. Yet it may be triggered by something you have set in motion, or something incoming, like a message. Sorry I do not know.
Am wondering whether you may want to reach out to Apple's Accessibility Support team for help with your AssistiveTouch question.
If so: See: How to contact Apple for help with accessibility features - Apple Support
All the best :-)