MyNetRu yes what is visible there is the extended details of the RouteNotFoundException exception, which is thrown when no file exist with this name and no Flarum page exists at that address.
When debug mode is disabled, this exception is automatically transformed into a 404 page.
So in summary, Flarum has no robots.txt file and debug mode should be off in production 😉
MyNetRu see https://discuss.flarum.org/d/8302-online-users-extension for an existing extension (that hasn't been updated to beta 8!) or please open a new discussion if you're looking for help developing your own extension.
