I have resorted to installing a snap for viber-unofficial. It works and solves the library problems (and the repackaging trick no longer yields a working viber). That is why snap was invented (or at least one reason)
However, there is still one problem. It needs permission to use the webcam. The askubuntu says you just give it permission. How to do that? They used the software center but that application is not available for ubuntu mate using the apt command.
The software boutique does not list the snap I installed.