This is another gradual rollout that was hitting some users recently. It will welcome you with a new overlay about "Starting new calls" introducing a new FAB. With that button, you can start an individual call or a group call. For group calls, you may notice a bit different layout to control its participants and video effects.
For now, it doesn't really look like a Material You redesign but very likely it will arrive at some point as well.
Google Duo – Apps on Google Play
High-quality video calling for Android & iOS phones, tablets, Google Nest & web.
