No, you don’t have to trust anyone. That’s literally the point of having secure protocols that don’t leak your personal data. 🤦
Unless you're reading all the code, understand the protocols, and compiling yourself you are placing your trust in someone else to do it for you. There's no way around this fact.
You suggest SimpleX, Matrix, and Briar (which I believe are great projects btw, I've used them all and continue to use SimpleX and Matrix) but have you read the code, understand the underlying protocols, and compiled the clients yourself or are you placing your trust in a third party to do it for you? Be honest.
I will agree though, if you absolutely do not trust Signal, you should use Briar or SimpleX, but neither are ready for "every day" users. Briar doesn't support iPhones so its basically dead in the water unless you can convince family/friends to switch their entire platform. SimpleX is almost there but it still continues to fail to notify me of messages, continues to crash, and the UX needs significant improvement before people are willing to put up with it.
The discussion in this thread is specifically about Signal harvesting phone numbers. Something Signal has no technical reason to do.
Let me give you a history lesson, since you seem to have no clue about where Signal started and why they use phone numbers. Signal started as an encryption layer over standard text/SMS named TextSecure. They required phone numbers because that's how encrypted messages were being sent. In 2014, TextSecure migrated to using the internet as a data channel to allow them to obscure additional metadata from cell phone providers, as well as provide additional features like encrypted group chats. Signal continued to use phone numbers because it was a text message replacement which allowed people to install the app and see all their contacts and immediately start talking to them without having to take additional action - this helps with onboarding of less technical users. Fast forward to today and Signal is only using phone numbers as a spam mitigation filter and to create your initial profile that is no longer being shared with anyone unless you opt into it.
Now, you can say they're collecting phone numbers for other nefarious purposes but they publish evidence that they don't. Will they ever get rid of phone numbers? Unlikely unless they figure out a good alternative to block spam accounts.
Privacy and security are not based on trust
You're 100% right. If you read the code, understand the protocols, and build the clients from source, you don't have to trust anyone 😊