Difficult situation.
I was in a similiar position. When I saw my non preferred guest made a reservation, I cancelled it.
Even though I cancelled with 10 minutes of their reservation, Airbnb blocked out those 5 days so I could not rebook with anyone else. I also have a stain on my record "Host cancelled within 24 hours of reservation." Not good 😞
In the end, I had to go to the guests and explain that my house was not appropriate for them (my poorly insulated house did not keep their midnight quarrels private)
My advice is to ask your guest to cancel. Give him some excuse. If he still is unwilling, sweeten the deal so he does cancel.
It's just money.
But don't risk your Superhost status if you can help it