The new Apple iOS 17 beta was released to developers earlier in the week and in the code MacRumors noticed a reference to an "Action Button." It offered nine potential functions the user could choose: Accessibility, Shortcuts, Camera, Flashlight, Focus, Magnifier, Translate, Voice Memos, and – crucially – Silent Mode.
This sounds a lot like a contextual button, which chimes perfectly with the rumors swirling that such a user-definable button will replace the physical mute switch. Even the name from the leak, Action Button, is already known from the Apple Watch Ultra, so it's excruciatingly plausible.
