Themed icons were one of the biggest parts of the redesign in Android 12, allowing Google service’s logos to match the overall look of your phone. Android 13 allows for dynamic app icons across third-party services for the first time, so you now won’t have to ruin the Material You design on your homescreen if you want other apps to be easily accessible.
Link: WhatsApp is the biggest app yet to adopt a themed icon for Android 13
via http://www.androidpolice.com