A few years back you provided some detailed information on the decentralised (or lack of nature) of a class of application. It may have been messaging devices.
Have you researched Element to be able to give a similar assessment?
I've used it a lot and researched it's background yes. Element is Discord-like chat app built on Matrix, a decentralised protocol for messaging. It's come a long way and I'd say it's now at a stage where it's a usable replacement for apps like WhatsApp and Discord, but it's just not as private as Signal currently as it comparatively lacks Sealed Sender, Private Contact Discovery, Secure Value Recovery, Private Giphy usage, etc.
However it's better than Signal for communication with people who you don't want knowing your number (although Signal are working on removing the phone number sharing requirement), for managing large groups (they have Spaces for grouping multiple chats together i.e. Discord Servers equivalent) and if you can't tolerate using a centralised platform.