Use: https://matrix.org

Support: https://edri.org

Technically, self hosting small private chat servers would be the correct answer. Even something as tiny, light-weight and simple as uMurmur running on ones router would suffice. Unfortunately however that will only work for close friends willing to join it. Others would need a strong incentive and that probably won't be a thing unless ChatControl leads to fines, cancelling people, cooperation from platforms such as Discord and Slack, transcriptions of private voice chats being taken out of context by AI and leading to jail time or even the inconvenience of people being perp walked out of their homes and places of work, mothers being arrested for sharing bath-time pictures of their kids leading to destruction of families, etc...

All of this is moot however should client side scanning occur and then so much more can be taken out of context. In that case people will need clients they fully control which excludes all manor of cell phones, Windows (recall), Mac (mediaanalysisd). Given cell phones exacerbate spending from those with a lack of impulse control I will attract vitriol from all the greedy business people by saying this. All the binaries and libraries required for client side scanning are already in place. It's just a feature toggle controlled by the OS maintainers at this point. One tiny OS update opens up a channel into everyone's world to be automatically interpreted by AI.

If enough people switched to Linux I would expect some obfuscated daemon to be inserted into systemd that purports to protect something.