Affects all Bedrock platforms on 1.8.1.
When creating a new survival world without cheats enabled, due to the world owner being defaulted to Member status, attempting to change the toggled world settings while playing in a world (non-cheat settings) fails due to the player not having the correct permissions.
When attempting to change the toggled settings (Friendly Fire, Show Coordinates, etc.) and exiting out of the settings menu, a message is displayed "Unknown command: gamerule. Please check that the command exists and that you have permission to use it."
The only way to change these settings is for the player to exit out of the world and change the world settings, or change their player status to Operator.