It’s taken a few years, but Picture-in-Picture mode in WhatsApp video calls is now also available for WhatsApp users on an iPhone. It arrived on Android in 2018 and had been in the beta of WhatsApp for iOS since the end of last year. Now, it is activated for everyone.
PiP mode, or Picture-in-Picture or “image in image”, it has been part of the Apple operating system since iOS 14, in 2020, but it is not until now that WhatsApp takes advantage of it for its video calls. Since WhatsApp 23.3.77 for iOS, it is possible to make a video call and keep watching your video while browsing other apps on your mobile.
Floating video call on iOS
If you answer a WhatsApp video call with your Android mobile and switch to other apps, the video call is still visible thanks to a floating window. The same did not happen in iOS, despite the fact that the operating system accepted it for a couple of years. The wait is over.
WhatsApp has added to the change list of the stable version 23.3.77 of WhatsApp for iOS many of the new features that we have been collecting in recent weeks: sending documents with comments, longer group names and avatars. It also includes the support for iOS Picture-in-Picture mode.

Thus, it is possible to change the app without pausing the video, seeing at all times both your camera and that of the other person in the floating window. This floating window uses the official iOS API, so you can move the floating window and temporarily hide it while using other apps.
If you use WhatsApp video calls frequently on an iPhone, this gives you more flexibility to be able to check something in other apps without losing sight of what’s going on in the video call. After waiting a couple of months since it hit beta, now everyone with WhatsApp, on iOS or Android, with or without betathey can use the floating windows in video calls
Via | WaBetaInfo