So, all of those communications you had with co-workers based on the promise they would be private until you were notified future ones wouldn't be anymore? Now it's ALL available to your employer.
Surprise!
(This is presumably due to GDPR)
If you want privacy use a private channel. Your employer's work tools don't qualify.
OTOH, I still think being paranoid is the safest policy, so if you're plotting to overthrow your boss, or sell secrets to your biggest competitor, I still wouldn't do it on the company networking, and/or using a company computer.
Cloak-and-dagger games are very similar to building your own crypto: likely to be broken at a fundamental level, never mind the amount of magic security glitter that you pile on top.
From the actual source: https://www.echr.coe.int/Documents/Press_Q_A_Barbulescu_ENG....
There are a number of things I might mention to a coworker over a private IM which wouldn't necessarily put my employment at risk, but would be awkward for management to suddenly have access to.
A couple made up examples:
"I'm super sick, but $boss is really pushing me to get the report out. I just want to go home and be sick all alone."
"I hate management's decision to reduce vacation days. No wonder we can't keep people around here."
"Did you see Tom's email? It's kinda awkward that he thinks he's a strong contributor to the group..."
Never write something you wouldn’t want printed on the front page of a newspaper.
You're begging the question.
"Competent and trustworthy" people won't abuse their power by definition. Anyone who abuses their power intentionally is untrustworthy, and anyone who abuses their power unintentionally is incompetent.
In the real world there are many incompetent and untrustworthy leaders. Slack has no choice but to operate in the real world.
They can also install screen capture and key logging software if they want, but that's less common and without disclosure is a lot shadier (although certainly legal in the US). I wouldn't expect it most places; it's a more extreme step.
But never trust encryption at work unless you know your company's policies.
Of course, you also need to trust your hardware.
And this is exactly end-to-end encryption that the original thread responder mentioned; I know it's in place so I won't connect to my personal accounts from the work machine. That's what my phone is for (and I won't use their wifi for my phone, either).
That sounds like a convenient marketing bullshit bogey man to me.
You have no right to privacy when you're inside your company's office using your company's computers to access your company's network. They own it all, you just have permission to use it within the guidelines they set and you signed off on when you were hired.
---- Edit ----
To clarify; my comment is referring to the novel 1984. While a bit tongue in cheek, it was not meant entirely as a joke.
This is a forum visited mostly by IT workers. I would assume most of us here know enough (or should know enough) to realize that any of our communications at work can be read by someone else and so you may want to treat it a bit as such.
In my personal programming working experience I have seen data captured in all of the following forms, reviewed, and then used to fire or prevent firing individuals.
Email, Instant messaging, Phone calls (audio recordings), Computer monitor (video recordings)