WABetaInfo has recently revealed that the next WhatsApp update will bring a redesigned voice call interface.

WhatsApp beta version 22.5.0.70 sports a new interface to make voice calls, with the feature available to beta users. Notable additions include a more streamlined view when users are participating in a group call.
The messaging app rolled out visible waveforms for its audio messages, and is now doing the same for its voice call platform. This addition makes the user aware of who’s speaking and who’s left their microphones on.
WABetaInfo has said that app developers are also bringing wallpaper into voice calls but it will be most likely integrated into future updates.
Lastly, the app is working to bring end-to-end encryption indicators to its messaging platform via visual additions. This ensures that end-to-end encryption is activated before they begin the conversation.
Currently, there is no exact date on when the feature will roll out to the public.