To get the Daily Briefing canceled I did what is mentioned in the first reply (Settings>Apps>Permissions>Daily Briefing). I had to reset my watch though to get the option.
It worked immediately, no 48hrs to take effect.
The funny thing is, I just checked the option and it is set back to On for some strange reason, and I still don't get the briefings (which is a good thing) ...
May be another reset will do the trick, but I'll wait until I actually have a problem before I reset my watch.
All other messages, like sleep reports, encouragements, etc are app related (at least they were for me).
If you go to the widget for the app, tap the screen, then tap the the 3-dot menu, then settings, you can switch the message off.