Yes, we are talking about the omemo-implementations.
First: We would like not to remove any support and therefore library. But nevertheless a second perspective would be good on that library. As that library is provided throughout Open Whisper Systems as they are connected towards the Signal Technology Foundation and they are funding the Signal Messenger LLC, who are developing the application and framework around Signal. You see already here (https://en.wikipedia.org/wiki/Open_Whisper_Systems) that there are many names within. But that's not only the point besides this strikes my personal critical perspective already.
About the library itself (here is the repository: https://github.com/signalapp/libsignal-protocol-c): It was marked as "archived" in February 2022. The newer implementation is nowadays done in Rust: https://github.com/signalapp/libsignal
Besides the point that Signal is anything but surely not oriented for "technical emancipation" sidewise for mobile devices. So all in all left: Either we stick with XMPP and therefore self-hosted, organized servers, tox or others. Likewise we would then need to look around for an alternative towards libsignal-protocol-c as you see again here an example where profanity and liblurch are using only one library essential and mandatory. But this library is not without critical points. Not only the group (company) behind (Whisper Systems prompted that Signal is all good, but nevertheless only most centralized), but also they seem to have ditched the C-implementation like others before. Hyperbola is oriented onwards that the user will be always in charge and command. The user installs the system, the user commands the system and the system is for sure NOT downloading further parts when building or running - only when the user commands it.
The free and libre community needs to review their used implementations. When we rely too much on questionable frameworks and more, we will loose everything for sure. That's the reason for HyperbolaBSD. Maybe it is very cautious, but better to stay in control for an operating-system in a whole. The alternative is to rely on implementations done first by groups transforming into so-called "foundations" bought and funded from companies. A real foundation is absolutely different towards, nothing negative on it. Staying in control and command is the vision and essential for Hyperbola. Especially therefore we are doing that much work with auditing the sources for our BSD-implementation. And especially therefore we are also oriented on free, libre licensed software. Sources have to be provided and making foul compromises like done with "asking for permission to modify" (Rust and others) is nothing we will ever do. In the end it is even not bad that the current library is marked as "archived", so it can be forked right away more easily and developed independent.
And especially our essentials for technical emancipation is the point we are very cautious about implementing more. We don't like the phrase "move fast, breaking things". We like: Move slow and preserve, but stay true and steady for values to have a system working for a really long time, even without being connected outside.
Yes, you have noted that this thread should be foremost only about XMPP and possible solutions. But bringing into my perspective from packaging and developing: This is most no longer possible as it is all connected. We need nevertheless (digital) safe spaces, where speaking is taken by word and people are honest together, with empathy and solidarity. The hope WAS (yes, past form selected) that free and libre software can bring this. But we have lost the course - from my point - by just seeking for the newest "stuff" instead of bringing a good fitting overall system together, so people feel safe and confident. Until we reach back to this point, we need to take care and also need to bring up the warnings. Because that's all I can do: Warn about the overall development. Communication counts, words are important, but they should be selected wise and not without meaning because all has lost its "meaning" and everything is for the "fun". That's a NO: Safe space, developing together in person and code, feeling well for a good system and preserve freedom, confidence and democratic points all together. Not what the "internet" is nowadays about: Seeking in simulated anonymous spaces (those do not exist) for just getting the own ego. Even when I'm not interested to bring my whole private life "online", I stay honest with my perspective and be nice to others for helping. About five years back I thought there is no need to write that down, but this has changed for sure and I'm glad we do it here different as we try hard.
Human being in favor with clear principles and so also for freedom in soft- and hardware!
Certainly anyone who has the power to make you believe absurdities has the power to make you commit injustices: For a life of every being full with peace and kindness, including diversity and freedom. Capitalism is destroying our minds, the planet itself and the universe in the end!