There is also a Japanese sentence that I don't quite understand: "No smoking in the meeting room". Why is this a "conference room" instead of a "conference room"

(18) It can generally be used to indicate the way, method, place, etc. There is a feeling of what is related to this condition, but there is a usage to indicate the scope. Smoking is forbidden in the meeting room. に is more inclined to the destination, so に is the most suitable to express the meaning of no smoking in the whole conference room. My grammar is only a rough idea, you can look it up in the dictionary again, I hope it can help you ~