on your own premises, for your own users/community in case you are not trusting Signal’s infrastructure.

Yes, that's an example of data (and infrastructure) sovereignty. It's good for self-contained groups, but is not general-purpose messaging, since it doesn't allow communication with anyone outside your group.

If you know any other similar alternative with strong encryption open source protocols please let me know! I love learning new things everyday!

Matrix can do this. It also has support for communicating across different server instances worldwide (both public and private), and actively supports interoperability with other messaging networks, both in the short term through bridges and in the long term through the IETF's More Instant Messaging Interoperability (MIMI) working group.

XMPP can do on-premise encrypted messaging, too. Technically, it can also support global encrypted messaging with fairly modern features, with the help of carefully selected extensions and server software and clients, although this quickly becomes impractical for general-purpose messaging, mainly because of availability and usability: Managed free servers with the right components are in short supply and often don't last for long, and the general public doesn't have the tech skills to do it themselves. (Availability was not a problem when Google and Facebook supported it, but that support ended years ago.) It's still useful for relatively small groups, though, if you have a skilled admin to maintain the servers and help the users.