Is it possible to ensure that only one document can be open at a time? My target is macOS 15. The idea would be that the user is alerted and no existing document can be opened (e.g. drag and drop, file->new, Finder etc).

I've tried everything I found on Google and none of these work:

• `.listRowInsets()`
• `.environment(\.defaultMinListRowHeight, 0)`
• `.controlSize(.small)`