The old news is that WhatsApp has been working on overhauling the whole UI of WhatsApp and move away from the old green accents and UI. WhatsApp has also been rolling out a better dark mode instead of greenish dark mode. 

Among all these one thing that's left for some change is the in-call UI. I am specifically talking about the bottom sheet UI here which hosts the video, speaker, mute and cancel buttons. Currently it looks like this - 

But WhatsApp might be working on bringing some much needed change in this UI. While messing around with WhatsApp to find if there is anything else WhatsApp might be working on, I stumbled upon this newer change. Here are some screenshots for comparison - 

As you can see the the screenshot the new UI gets rid of the swipe up sheet for the buttons. All the buttons are now hosted in a single circular rectangle and if you see closely, the icons have been also replaced with a filled version of icons. There are other changes as well like when you change a audio call to video call, the requesting interface will look like this -

As you can see the change will bring a consistent UI across the whole calling interface. The bottom sheet on video call interface will look like this -

Looking at all these changes, it seems like WhatsApp is still working on this as because some things have rough edges. Like the 3 dots icon ••• , tapping on it does nothing. There are some issues with background color as you can see in swtiching to video request interface. 

There is no timeline for roll-out of such changes and we might see them rolling in beta version whenever they are ready.