If we're talking about Matrix as a Discord alternative, then that would mean thousands of channels, each with hundreds or thousands of users, many with constant activity.
I'm not sure if anybody actually uses Matrix at the scale of the average Discord user. Sliding sync is supposed to help, but I don't think the Matrix architecture can realistically scale that high.
I set up their accounts
Setup is the hardest part. Syncing multiple devices and device migration are also hard. I'll bet you're going to act as tech support every time they get a new phone. That's fine for your family, but it's hardly going to scale.
The performance issues show up when dealing with large groups syncing between instances. You might just not be using it that way, but that's what needs to work seamlessly for a viable substitute for Discord.
Matrix is notorious for its poor performance with large/numerous groups. They keep claiming to improve it, but it's still bad.
I mean, it's great that it works for you, but be honest: isn't your tolerance for technological friction a bit higher than the average bear's? People complain that Mastodon is too hard, and Matrix is ten times worse to sign up for and use.
I hate to say it, but Matrix is never going to be mainstream. Its UX is bad and it seems like it's too bloated to fix. If I tried to get people to move from Discord to Matrix, they'd never take me seriously again. It was hard enough getting people to move from Facebook Messenger to Signal.
Also interested in this. The ideal solution would stream to a private server for storage in real-time, with access control so you can grant trusted individuals access.
This would allow retention of evidence in a scenario where your phone is seized/destroyed/lost or you are detained, and would give you (and whoever you choose to grant access) the ability to control distribution, unlike a livestream to Twitch or YouTube or whatever.
FOSS projects are often labors of love.
Nobody who isn't completely deranged loves marketing.
I've been using cryptpad.fr (the "flagship instance" of CryptPad) for years. It's...fine. Really, it's fine. I'm not thrilled with the experience, but it is functional and I'm not aware of any viable alternatives that are end-to-end encrypted.
It's based on OnlyOffice, which is basically a heavyweight web-first Microsoft Office clone. Set your expectations accordingly.
No mobile apps, and the web UI is not optimized for mobile. I mean, it works, but does using the desktop MS Office UI on a smartphone sound like fun to you?
Performance is tolerable but if you're used to Google Sheets, it's a big downgrade. Some of this is just the necessary overhead involved in an end-to-end encrypted cloud service. Some of it is because, again, this is a heavyweight desktop UI running in a web browser. It's functional, but it's not fast and it's not pretty.
Or perhaps you do not understand how Discord is commonly used.
People join dozens of servers. Maybe one for every game they play, every TV show they watch, every podcast they listen to. Everything has a Discord.
Even small Discord servers have many channels. Bigger ones will have dozens or hundreds of channels.
Some servers have millions of users. Most of the servers I'm in have thousands.
Many channels are default for all users in the server.
Not sure what the mathematical average is, but this is certainly common at least, and any alternative that can't handle this is no alternative at all.