TL/DR:
- Yes, the content of your conversations is fully encrypted
- Meta (aka Facebook) still has access to the metadata: who you chat with, how long you chat, your phone’s battery level, stuff like that
- You could use Signal to have even better privacy, but your contacts might not use Signal
Apple
- Focusing on health information specifically (their recent marketing campaign), it’s true that Apple end-to-end encrypts your health data
- However, other apps may not
- Third party apps can request (from you) access to your health data
- Be skeptical of them
I left signal when they dropped SMS support. It was just the last straw in a line of changes that showed they didn’t give a shit what their users thought.