Maybe the real source of complexity in that flowchart is there are just too many ways to suppress notifications. You have muting, do not disturb, do not disturb overrides, @message preferences per channel and global, DM preferences, and so on. I love dials and knobs and sliders in my software, but at some point when they are all for the same feature, there is no longer any way for the user to intuit how they interact…
Does the complicated flowchart point to deficiencies in the Slack user interface? If the user cannot intuit the flowchart, then how can they (as several sibling comments rightly point out) reliably turn notifications on or off?
Algorithmic transparency should be a thing, no?