Script disabling parts of the CoreGui lacks permission?

For my game, i want the backpack to be hidden (Because the game uses gears that i don't want to be visible.)

However, whenever i want to disable parts of the CoreGui, the output prints this: The current identity (2) cannot Class security check (lacking permission 1)

The script is placed inside the Workspace. I already tried putting it in the ServerScriptService, ReplicatedFirst. But they all give me the same error.

The game is FE. But i'd rather not use any RemoteEvents or RemoteFunctions, because i already have allot of them in my game.

Maybe there is a way to give a script higher permissions?

Any help is appreciated. Thanks.

Put it into a local script inside StarterGui.