Whatsapp continues to work on adding bug fixes and new features for the Windows native application. Following the addition of screen-sharing functionality, WhatsApp is now making a few small adjustments in relation to missed calls. A "Call back" button that shows in an event message when a call is not answered is the new feature, according to WABetaInfo.
As per the screenshot shared by WABetaInfo, the “Call back” button is now visible in the event message generated when a call is missed on WhatsApp.