Why is there a New Game Plus when Halo ODST doesn't have one, Are there skulls you have to activate? personally I don't know

Hey, so New Game is considered a "fresh disk" on a "fresh Xbox profile". In this scenario you would not have any audio logs collected. New Game+ is when the player has played Momabasa Streets and has collected 1 or more audio logs.

Because you can't un-collect audio logs (without creating a new player profile which isn't always possible) runners have decided that the main source of Halo Speedrun leaderboards, HaloRun.com, will track NG+ runs. SRC is used to track the remaining NG+ difficulties as well as the New Game category which some people have expressed interest in running. They would need to start the game on a profile that has 0 audio logs collected but can collect them during the run.