Nobody even mentioned the game mode thing, so I will.
Basically, maps were removed in v21, and were replaced with game modes.
You could still choose a custom game mode for dedicated servers, by putting -gamemode [game mode name] at the end of the "Target" thing.
Like, if I wanted a dedicated server with the freebuild game mode, I would type this: [bl launcher] -dedicated -gamemode Freebuild.
If there's spaces in the game mode name, replace those with underscores. For example, if I wanted a dedicated server with the Pirate DM, I would type this: [bl launcher] -dedicated -gamemode Pirate_DM