@Elisabeth447 You can and must report a guest who has threatened you in some way to Airbnb.
Who are these "dangerous" guests you are getting (not their names, but how are they managing to book your place?) and in what way do you consider them to be dangerous? Have they threatened you? Had guns? Dealing drugs out of your property?
You can still review them to warn other hosts. Guests cannot see the ratings they are given, so mark them 1* across all categories and "Would not host again", which they also can't see. Then leave a written review which is "coded"- like simply "Stayed 2 nights". Most other hosts will understand that you had nothing good to say.
You have a lot of lovely reviews, but I have to say I was shocked by your response to the guest who said she was questioned as to why she was wearing a mask while in communal kitchen space. First of all, it is extremely rude of you to question a guest who is trying to follow safe Covid precautions. Then you claimed that neither guests nor hosts are privy to Airbnb's policies on this, which is completely untrue.
In fact, they state that hosts and guests should wear masks in communal spaces. Yet you told her that no one else has felt the need to wear a mask, as if she were doing something unacceptable.
Talking about dangerous, I would consider your listing to be a dangerous place to book re Covid.