Free and Open Source Software

It's a relatively complicated question with no "correct answer" but I'll do my best to boil it down in a quick post.

Signal is probably the best option. It's easy to use and easily the most widely-adopted, and basically sets the standard for security, with most other private messengers using the same protocol for encryption. The most common criticism is their requirement for a phone #. However this also makes it the easiest to connect with people, and it's the reason why I regularly communicate with a dozen IRL people like family and friends. I know literally no one else who uses any other private messenger, personally. I'm not sure what you mean by "numbers are blocked".

SimpleX is also relatively easy to use, feature-complete, decentralized and more private and resilient than Signal. Doesn't require a phone number and doesn't really have any identifiers whatsoever. Downsides are you need to know someone already uses it and you need to get an invite code somehow to message them. Upsides are absolutely zero spam, for the same reason.

Next is "chatmail" (DeltaChat, ArcaneChat, etc.). This has tons of cool features and is also decentralized and easy to use.

Matrix I'm going to argue is too difficult to use, both from the user and server standpoint. And I'm not going to argue about it, so don't @ me.

XMPP is very old and mature, but also fragmented and more complicated to use, with various encryption protocols. It's fine.

So if you're looking to add friends and family to a new chat platform, I recommend SimpleX. Otherwise, it's Signal.