WhatsApp is working on increasing the number of participants in Group video call. The feature is reported by Wabetainfo and is under development. This feature is currently disabled on WhatsApp beta version 2.20.128 on Android. The update is already available in WhatsApp beta version 188.8.131.52 on iOS platform.
As Wabetainfo reported, the group video call limit is to be more than 5 users in a call(expected). In quarantine, people are making video calls often to stay connected with friends and family. GoogleDuo has also increased video call limit up to 12 participants in a call.
WhatsApp also adds video call options in each group to make a call directly from the group. If you have updated WhatsApp to the latest version; then you may face issues in making group video calls. The feature is not available yet, but soon it will soon be rolled out in an update.