SetCoreGuiEnabled is not a valid member of PlayerGui "Players.Player1.PlayerGui"

[midnight beacon]

Yo, long time no help

It should be:

game.StarterGui:SetCoreGuiEnabled(Enum.CoreGuiType.Backpack, false)

Sure you can, not to change GUIs for players, but you can use StarerGui to turn on and off Core GUIs

The script? or what

If you are talking about the script location, then it can be everywher a local script works

Show the code

Instead of having a script that is moved around and enabled/disabled, create a system

function turnBackpack(bool)
  game.StarterGui:SetCoreGuiEnabled(Enum.CoreGuiType.Backpack, bool)
end

turnBackpack(false) --as default maybe

--using remote event or any kind of event turn on backpack

Maybe not

Explain what you are trying to do

And you want to keep moving that script to another tool or what?

So you are doing a handcuff system, right? Why dont you add a boolean value for each player to be true when handcuffed and false when not
Then you are just gonna use changed on that boolean to chance backpack on or off

Having a script to be moved (/cloned) and to be enabled/disabled is not the best idea

Could you send this script?

one local, one server and one remote event for targetchar

Local script:

local remote = script.Parent:WaitForChild("RemoteEvent")
local tool = script.Parent
local player = game.Players.LocalPlayer
local mouse = player:GetMouse()

local boolValue = PLAYER_BOOL_VALUE

tool.Activated:Connect(function()
    local target = mouse.Target
    if target == nil then return end
    
    local player = game:GetService("Players"):FindFirstChild(target.Parent.Name)
    if not player then return end
    
    local targetChar = player.Character
    
    local distance = (tool.Parent.HumanoidRootPart.Position - targetChar.HumanoidRootPart.Position).Magnitude
    if distance > 8 then return print("Sei troppo lontano!") end
    
    remote:FireServer(targetChar)
end)

function turnBackpack()
  game.StarterGui:SetCoreGuiEnabled(Enum.CoreGuiType.Backpack, boolValue.Value)
end

boolValue.Changed:Connect(turnBackpack)

Server Side:
Here you would need to run OnServerEvent and do all the checking, handcuff the player, change target player boolvalue to true if cuffed and false if not

Hm... I dont think so