I use pseudonyms and post weird shit online, but I still feel very reluctant to post anything on large public channels inside a company. Everything is tied to your real name and all of us are hyper aware now that every single fucking thing on the internet is monitored, and will be used against you if necessary. I am 99% confident a tool already exists that a manager can use to get all messages from employee X over the last N months and summarize the content and surface any "red flags", which in a corporate setting would be incredibly broad.