There you can also add participants to the call after it is started to convert it into a group call. This update should be available to everyone already or will roll out very soon.
Thanks to @Skyking469 for sharing!
Tester Context:
- 📲 WhatsApp is a popular messenger app by Facebook.
- 📲 WhatsApp is also available in Beta and you can opt-in as a tester via Google Play.