to add even more to what’s already been said, even if Signal’s infrastructure was compromised and they could see messages traveling through their servers, each one is encrypted, the keys are rotated with every message (cracking one, which is nearly impossible, doesn’t give you access to previous or future messages), and thanks to Sealed Sender, only the recipient knows who a message came from. There are many other layers that they’ve engineered to ensure they can’t know anything about you, like private contact discovery, using secure enclaves, remote attestation, etc.