simplex is a relatively new chat app but it's evolving pretty fast, i suggest it too, but it has several bug and missing feature that need to be fixed and added in order to make it like a standard chat application
the call will close if you go back to the chat (they should fix that in the next version)
it does not ring while you call
it can only be synced to a one desktop via the wifi
it has only local notification system (due to security reasons)
the calls are pretty susceptible to the line stability
but seems the only real secure chat app out there, you can check out the roadmap in the description of GitHub
it's not centralized, you can choose your smp, xftp and webrtc ice servers, or you can install them in your own server
so is a decentralized chat application
so far i was able to do calls and videocalls to everyone (i have 8 friends there), but i won't say that the calls are stable, the application needs time to stabilize, and that's what they are doing, you can check the the GitHub page or chat with the developer if you want to know more
I have used SimpleX Chat for a few months and the following made me switch to XMPP:
It literally drains my battery on my Google Pixel 6a with GrapheneOS. I had to charge my phone 1 time per day. Before and now after, I only need charge my phone 1 per 2 days.
It is "impossible" for me to connect SimpleX Chat on Linux. Haven't tried on Windows because I don't use that shit due to privacy reasons.
If you're in a voice call and goes back from the call to send something in the chat (like a picture), the call will end. You are not allowed to use the chat while you're in a call in SimpleX Chat.
Simplex chat is good for group chats. The battery life is fine as long as you switch it to periodically check for incoming messages. Calls will break but they are already completely unstable so its not a big deal.