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.

Jon ran a poll on Mastodon with regards to what linux packages people mainly use.

722 votes =
58% DEB
43% Flatpak
24% RPM
7% Snap

Jon also mentions Flatpak specifically:

At @Vivaldi we clearly like to support the packages our users want. At the same time adding packages is not just a question of making the packages, but also a question of testing, which can be quite time consuming.
The issue with Flatpak is that the Flatpak sandbox requires us to disable the Chromium sandbox, which is not optimal.
If there is a way around that, that would be great!
Disabling the Chromium sandbox is a potential security problem and requires changes in Chromium.
Source

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

Changelog

[New][Mail] View Filters are confused for being a Mail Action Toolbar (VB-95308)
[Address bar] Engine icon is often not displayed in search field (VB-94157)
[Address bar] Search Field dropdown remains opened (VB-98720)
[Address bar] Emojis as favicons appear blank (VB-81544)
[Address bar][Bookmarks] Display folder nickname (VB-98925)
[Calendar] Subject of event not visible in the reminder window (VB-98736)
[Chromium] Upgraded to 116.0.5845.59
[Crash] When adding vivaldi://discards as a speed dial (VB-98877)
[Downloads][Panel] Google Safe Browsing causes downloading to get struck (VB-96539)
[Feeds] Icon disappears when page loads (VB-50729)
[History] Shows http entry after https entry on a redirect (VB-26114)
[Keyboard] Cycling focus stuck when tab bar is hidden (VB-95976)
[Keyboard] Focus Panel Controls has stopped working (VB-93688)
[Linux] Vary Process names to ease use of tools like killall and top (VB-99065)
[macOS][Media] Poor video performance (VB-81757)
[Mail] Cannot mark all mails as read in custom folder (VB-94347)
[Mail] IMAP folder names not decoded from UTF-7 (VB-98829)
[Panels] Closing floating web panel hides the sidebar unexpectedly (VB-98621)
[Panels] The scroll bar is covered by the side panel handle when it is set on the right side. (VB-98065)
[Panels][Workspaces] Not all Workspace functionality is available in the Window Panel (VB-98479)
[Performance][Clock] Button can slow down the creation of tabs (VB-83297)
[Performance][Downloads] Progress animation stresses GPU (VB-98841)
[Spatnav] Box is moved on scroll (VB-89443)
[Speed Dial] Fast bookmark drag+click may block pointer events (VB-98930)
[Workspaces] Button title spacing wrong (VB-99111)
[Workspaces] Loudspeaker icon on Workspace tab keeps appearing and disappearing (VB-97425)
[Workspaces] Make sure tab opens in the last-open workspace when started (VB-96702)
[Workspaces] Moving tab to new window switches workspace in existing window (VB-98804)
[Workspaces] Replacement tab from root workspace moved into active workspace when moving original tab in Window Panel (VB-99014)