Okay, fair enough. I do agree it's ambiguous, but I don't draw the same conclusion.
Is that because you don't accept what Todd Howard and Christopher Nolan said about the timeline?
I think it's somewhat ambiguous. It lists the fall as 2277, but then there's an arrow to the mushroom cloud. So it doesn't say it was nuked in 2277, but it doesn't actually say when the nuke occurred either. But Todd Howard says New Vegas is canon and the nuke came after, so that pretty much answers the question, doesn't it?
IGN had an interview with Todd Howard and brought up the confusion and he said the events of New Vegas are canon and that Shady Sands was bombed after 2281. The sign outside Shady Sands in the series also refers to it as the first capital of the NCR, which would imply there's at least one other.
https://www.ign.com/articles/fallout-official-timeline-confirmed-how-the-show-fits-in-with-the-games
If you haven't already, you can try the MUC search at https://search.jabber.network.
It looks like everything is operational and federating with the wider network at this time. Hooray!
For Linux and Windows, gajim works very well and is easy to use. It definitely doesn't have an interface from 1995. If you need something easier for people on Linux, dino is even more streamlined and is extremely easy to use. I think there was an effort to make a Windows build too, but I don't know how far along that is or if they are still working on it.
For Android Conversations is the gold standard. On macOS there's Sikin and Monal, but I've never used them since I'm not a Mac or iPhone user. But all these clients support a wide variety of features including encryption.
I'm not sure I follow you on this point. XMPP has had MUCs (Multi-user Conferences) which function similarly to chat rooms/IRC channels for a long, long time. The channels are accessible regardless of what server you're on as long as your server is federating with the wider XMPP network. There's even a searchable list of public MUCs at search.jabber.network covering a variety of topics. Most servers allow creating new channels if you want to start a new one, and anyone can join regardless of their server.