It appears that Slack v 4.27.154, which was released 3 days ago, isn't working for some users, and the official workaround from Slack support is to downgrade to an older version. We right now have 4 questions about this:
this answer to the first question listed seems to be the most detailed, although it only describes how to do so for apt packages, not deb or flatpak ones.
Can we get these closed as duplicates?