The reliable netizen who previously accurately broke the news about the features of Dynamic Island recently posted again on the MacRumors forum, sharing information about the customizable Action Button.

The sources say that the iPhone 15 Pro and iPhone 15 Ultra (or iPhone 15 Pro Max) models are moving away from the mute paddle that has been on the side of the phone since 2007 and replacing it with an Apple Watch Ultra-like Action Button that allows users to customize it in a variety of ways based on their preferences.
MacRumors has also shared the customizable options for the Action Button, which is listed below:
Toggle ringing and silent status
Enable/Disable Do Not Disturb mode
Enable/Disable Flash
Enable/disable power saving mode
Toggle light / dark theme
Enable / disable rotation lock
Show home screen
Show lock screen screen
Open Control Center
Open Notification Center
Open Camera
Screenshot
Record screen
Run a shortcut
Show multitasking view
Show App Library
Launch Shazam, a song-listening service
VoiceOver
Launch Compass
Change background music
Most of these Action Button functions are now available through the Back Tap feature. Introduced in iOS 14, this feature allows you to trigger specific actions by tapping the back of your iPhone. This feature can be set in the Settings app under Accessibility → Touch → Back Tap. Settings.