I really wish I knew what this badge meant in Messages. I can’t stand having badges and am diligent when it comes to clearing them. I CANNOT MAKE THIS DISAPPEAR!
Update: The number indicates how many messages apps are on your phone that you have not yet enabled at any point. Simply enabling them by hitting the elipsis icon will make the number disappear. You can then disable them and the number will stay gone.
This is not an obvious thing in any way and no reasonable person would ever correctly assume the purpose of it. Oh well, at least I’m satisfied and it’s removed.
Here is the source conversation, including the help I received.