Keybase was popular with some Hacker News users for a while, but now that it's owned by Zoom, anyone concerned about privacy ought to think twice before using it.
XMPP might be worth considering if you're hosting for yourself and all your contacts. I suggest avoiding it for public use, mainly because features are piecemeal and coordinating them across everyone's clients and servers is a bit complicated. (Also, I don't know if there's a good XEP for encrypted search.)
Back when encrypted search was being developed for the Electron app, I think someone had it working in a standalone browser as well. Perhaps that was with the help of a browser add-on; I don't remember for sure. I suspect github.com/t3chguy would know, as he seems to be active in discussions of that feature. It might be worth asking him about it.
Does it have feature parity with Element yet?
Not yet. It's in beta.
https://element.io/labs/element-x
EDIT: Nheko is NOT a mobile client.
If you specifically meant mobile, you could have said so. Your statement was, "every other client has even more drawbacks when it comes to E2EE." Nheko disproves that statement. It also suggests that some alternative mobile clients might handle E2EE at least as well as it does. You might want to try them.
By the way, text search with end-to-end encryption happens to be tricky to implement, and Matrix projects aren't funded by corporations with deep pockets. Tempering your expectations regarding development speed is probably worthwhile here.
Correcting some misconceptions...
Element for Android doesn’t support searching in encrypted channels
That's true of regular Element for Android, but it's being replaced with Element X (which is built with Rust). I would expect search to be added there if it isn't already.
and I think you can’t use E2EE in the browser at all(?)
I have done it in Firefox, so that's false. Perhaps you had trouble with a specific browser?
plus basically every other client has even more drawbacks when it comes to E2EE.
Nheko handles E2EE just fine, so that would seem to be false as well.
Since you're looking for recommendations, it would help if you said which clients you tried and what problems you had with them.
In case you haven't seen it, you can set a Features: E2EE filter on this list:
https://matrix.org/ecosystem/clients/
Not really an answer to your question, but just to make you aware of some options:
Have you considered using subkeys for each of your machines, signing things with those, and keeping their master key someplace safe? That would limit your exposure if one of those machines is compromised, since you could revoke only that machine's key while the others remain useful (and the signatures they have issued remain valid).
Are you setting expiration dates on your keys? That can bring some peace of mind when you lose your key/revocation data.
I just learned about that as well. I hope Larian dilutes or buys back Tencent's shares.
Five-year-olds must be pretty advanced in the 24th century.
These come to mind:
So with normal use it should be fine for a few decades.
Considering that "normal use" can be so very different among different people/applications/climates, I don't put a lot of stock in assessments like that, but it is at least one prediction to compare against when we see what happens in practice. Time will tell.
I'm curious how long the current gen OLED consoles will be in use before they develop screen burn-in.
Whether to use encryption is a per-room setting, not per-server. It's controlled by the person who creates the room, not the server admin. It's on by default, and cannot be switched off later.
Rooms can be created without it because that makes sense for large public rooms, like those migrating from IRC, where privacy would defeat the purpose.