well, after initial problematic extra issues which involved doubts about how much space which instruments need , the official Dutch authority is now using a norm of 2m ( instead of the 1,5 between wind instruments), around each wind instruments and similar for singers (that situation is still being researched)
The special protocol involves also measures for a substantial air refreshing in a closed space that cannot be naturally ventilated.
Much incomprehension about this and other situations is caused by the fact that there seems to be a lot of unclarity about fitting many people in a room (up to 30 are allowed anywhere now but more are allowed on a plane) .
The type or air refreshing, filters and the compulsory use of face masks all make the airplane situation different.
The problem however is also the audience. No more than 30 people are allowed in one room, a big band can use up the entire allocation.