"We fly our rockets from the military firing practice area ES D 139 in the Baltic Sea, 20 km east of of the Danish island of Bornholm. It spans 70×35 km, and are opened to us by the Royal Danish Navy for the launch time window. The Danish and Swedish authorities are very helpful, and close the airspace above for airtraffic in the hours of the actual launch."

https://copenhagensuborbitals.com/about-us/

There is this quote: "If all of your money is not get wasted to your hobby, your hobby sucks."

Updated: "...and won't require closing air space..."

Maybe the military just informed airlines that they are doing tests in that area?

(I have no idea how air traffic control works)