Not the CoreGui that disables it. I'm asking about HOW I would I hide it. Thank you very much.
Make an LocalScript in for example PlayerGui and place this in it
EDIT: You can't hide it witheout using coreguis. Calling this function is hiding this and Backpack is still a object of player, but player cant access it. So player cant see them, but You can know which items has he got. If You want to hide gui and make items accesible by hotkeys then You just need to disable backpack coregui and make Your own script.