Let’s give credit where it’s due: https://github.com/maybenot-io/maybenot
The Maybenot Framework (FOSS) is how Mulvad pulls this off, and if you run your own VPN you can use this too! Mulvad is a contributor (and funder), so good on them.
Edit: for those interested, Mulvad’s client is a fork of Wireguard with Maybenot incorporated as a submodule. Cool stuff: https://github.com/mullvad/wireguard-go
So is Matrix and it’s way more popular. But recommending anything other than Signal at this point is a waste. Fediverse chat is a more complex conversion for many who are still in the connect via phone number stage for chat. Fediverse is an easier story for other platforms.