Exactly as expected, Apple sent the iOS 12.1.4 update which came to solve the FaceTime bug that appeared a week ago - see this link- The update came with one feature, which is to close the loophole that enables anyone who talks with you "group chat" to open the camera before calling, and Apple then stopped group conversations to close the loophole.
According to Apple's release notes, the iOS 12.1.4 update is a security update for FaceTime, and Apple's system status website explained that group FaceTime chats have returned to work again on condition of an update.
To update your device, take the following steps ...
1
Go to Settings -> General -> Software Update, it will show you that an update is available.
2
You can click on Learn more to view the update details.
3
To download the update, you must connect to the Wi-Fi, and it is preferable to connect your device to the charger, then press the "Download and Install" button, and the terms and conditions will appear to you, then agree to them.
4
After the update is finished, the device will restart. After several steps, the update will be completed.