Okay, because it's becoming very relevant: Let's talk about secure communications in the digital age.
It is important to understand one thing very clearly: There is not now, and has never been, a completely secure form of communication. Admittedly, this is alarmist and paranoid, but as Philo Gant put it, "Paranoia is just reality on a finer scale."
"Secure communication" is like "safe sex". There's always a risk. You could be speaking to someone in a code that only you and they know, in whispered tones, while floating naked in the middle of a lake 200 miles from the nearest person, and there is still the risk that you or they will be compromised. So let's talk about those risks.
When you communicate with someone, that message goes through multiple areas.
The connection between you and the server.
The connection between the server and your recipient.
So let's break these down and talk about the risks at each phase.
You. Arguably the most and lest secure part of this chain.
You trust you, obviously. But if you don't know how to keep your mouth shut, you're the biggest risk to yourself.
Gonna be honest here, if they get their hands on your PC, they can get into any data you have on it unless you use extra protection. This includes secure messaging apps that keep a history.
If your phone can be unlocked with your fingerprint, face recognition, or retinal scan, it might as well be unlocked. Anyone who gets their hands on your phone can just physically force you to unlock it. (And might not need you there-- you leave your fingerprints everywhere, and modern hi-def photos can be used to fool them.)
Fun fact: The Supreme Court has ruled that this is legal.
A passcode-locked phone, on the other hand, is STARTLINGLY hard to get into, with the trade-off that too many attempts will wipe your phone. (This makes it MUCH more secure, but ANNOYING.)
The connection between you and the server:
This can be monitored freely. The good news is that the INFORMATION is probably encrypted; even Facebook does this. But the fact that the data has been transmitted is not; your ISP may not know what you are saying, but they know that you are, for example, talking to Facebook.
The monitoring for this can happen at both ends-- they can be watching who you are communicating with, or they can be monitoring who is communicating with the server.
(This is honestly more of a factor when it comes to specific websites-- nobody cares who's visiting facebook, but they might be interested in who's visiting burndownthepatriarchy.com. Or, if you specifically are on their radar, they might be interested in which websites you are visiting.)
Sure, general communication with Facebook might not be interesting, since you can't tell a shitpost from a bomb recipe when it's encrypted, but Facebook admins can pull your history. And the government might ask them to do so.
The connection between the server and your recipient.
Same as above, but they might be watching the recipient.
Same as your device, except you're trusting the recipient to secure their phone properly.
Okay, all the data security in the world won't help you if it's a cop on the other end. Or a snitch.
I'm gonna plug Signal as an app that I love, because it's end-to-end secure; they can't pull the messages off the server. But it's worth noting that several of the Capital Rioters went down because they bragged to their friends over Signal or other secure apps, and their friends just took screenshots and sent them to the FBI.