How Private Really Are Encrypted Apps on an Android or Apple Smartphone?

Hi all,

So I'm really trying to do better with my online privacy, and have taken a lot of steps thus far. My newest step is encrypted apps like Signal instead of Whatsapp, etc. But I have a few questions, as a noob.

Firstly, Whatsapp maintains it is encrypted - but what does that actually mean? Can Facebook see my messages, if they want? And therefore what exactly is the difference between something like Signal and Whatsapp? I'm assuming Facebook …

android apple apps encrypted privacy smartphone