How to make a main menu that only appears when the player joins the game for the first time?

Hello, Your LocalScript is fine!

But if we want to know if the player had joined once and is returning, whe use something called DataStore, DataStore is a service that allows you to save a table or value forever!

Create a Script in ServerScriptService and call it whatever you want

If the script works, I'd highly appreciate it if you accept my answer, otherwise if it doesn't work, comment the problem and I'll try and fix it!

Script in ServerScriptService:

local PlayersService = game:GetService("Players")
local dataStoreService = game:GetService("DataStoreService")

local joinDataStore = dataStoreService:GetDataStore("JoinDataStore")

PlayersService.PlayerAdded:Connect(function(player)
	
	local isOnMenu = Instance.new("BoolValue")
	isOnMenu.Name = "onMenu"
	isOnMenu.Parent = player
	
	local playerJoinData = nil
	
	pcall(function()
		playerJoinData = joinDataStore:GetAsync(player.UserId.."-joinData")
	end)
	
	-- If player had joined once!
	if playerJoinData ~= nil then
		
		isOnMenu.Value = false
		print("Returning player")
	else
		isOnMenu.Value = true
		print("New player")
	end
	
end)

local bindableEvent = Instance.new("BindableEvent")

PlayersService.PlayerRemoving:Connect(function(player)
	
	pcall(function()
		joinDataStore:SetAsync(player.UserId.."-joinData", player.onMenu.Value)
	end)
	
	bindableEvent:Fire()
	print("Saved!")
	
end)

game:BindToClose(function()
	while #PlayersService:GetPlayers() > 0 do
		bindableEvent.Event:Wait()
		wait()
	end
end)