CharacterJumpHeight determines the starting value of Humanoid/JumpHeight for a Player’s Player/Character|Character. The value of this property defaults to 7.2 studs.

This property is only visible in the Properties window If StarterPlayer/CharacterUseJumpPower is set to false, as it would not be relevant otherwise.

Since this property is only relevant for characters being spawned in the future, changing it will not change any existing player characters. Changes to this property will only take effect when a player respawns.