I would like to know if the "everyone" alerts can be turned off and if so where, because I personally find them annoying and that I don't always pay attention to each announcement where the "everyone" tag is used.
Afraid you can't. They're used to highlight important items on Administrata. I try not to overuse them in my opinion, but I could always be mistaken. Some people may dislike them, while others find them informative.
If there's enough demand, I could set up an additional member group that’s excluded from the "everyone" alerts.