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Oh,forgot to mention there is support for sharing screen and separate window on desktop. Unsure about mobile clients.

If those you wish to have a video call with already have each others phone numbers then Signal is a option. It supports up to 40 participants. Available on Android, iPhone, Windows, Mac and Linux.

Signal has other great chat/messaging features too.
Also a unofficial community on Kbin

For me Ultramarine seems like it’s main thing is to offer Fedora with patent encumbered software included ootb. I.e rpmfusion enabled and probably some other bits and tweaks.

The Ultramarine team aims to make Fedora a little more user friendly by allowing users to install or package any software they want as long as someone maintains it in either RPMFusion or the Ultramarine repository.
Source

They do mention under planned features

System configuration application similar to YaST

So that could be interesting and combined with rpmfusion ootb help ease new users into the Fedora side of Linux.