However, employers can forbid you from using their facilities or property to facilitate these conversations.

Even if you're on company time, using company facilities and company resources, you have the legally protected right to discuss working conditions with other workers. It doesn't matter if you're using the company's Exchange or Matrix server to do so or not.

I’m afraid you are mistaken. I hope you are not confidently spreading this false information to others as it could put their jobs at risk.

https://apps.nlrb.gov/link/document.aspx/09031d4582ec1a7e

Thanks for the correction, I wasn't aware of this decision.