Flying scripts keyless (read in my description)

-- LocalScript under StarterGui (only one script needed)

local player = game.Players.LocalPlayer
local character = player.Character or player.CharacterAdded:Wait()
local humanoidRootPart = character:WaitForChild("HumanoidRootPart")
local UIS = game:GetService("UserInputService")
local runService = game:GetService("RunService")

-- GUI creation
local screenGui = Instance.new("ScreenGui")
screenGui.Name = "FlyGui"
screenGui.ResetOnSpawn = false
screenGui.Parent = player:WaitForChild("PlayerGui")

local button = Instance.new("TextButton")
button.Size = UDim2.new(0, 120, 0, 40)
button.Position = UDim2.new(0.5, -60, 0.5, -20)
button.Text = "Fly Mode"
button.BackgroundColor3 = Color3.fromRGB(0, 170, 255)
button.TextColor3 = Color3.new(1, 1, 1)
button.Font = Enum.Font.SourceSansBold
button.TextSize = 20
button.Draggable = true
button.Active = true
button.Parent = screenGui

-- Fly logic
local flying = false
local flyConnection = nil
local moveDir = Vector3.zero
local bodyGyro, bodyVelocity

local function startFlying()
	character = player.Character or player.CharacterAdded:Wait()
	humanoidRootPart = character:WaitForChild("HumanoidRootPart")

	bodyGyro = Instance.new("BodyGyro")
	bodyGyro.P = 9e4
	bodyGyro.MaxTorque = Vector3.new(9e9, 9e9, 9e9)
	bodyGyro.CFrame = humanoidRootPart.CFrame
	bodyGyro.Parent = humanoidRootPart

	bodyVelocity = Instance.new("BodyVelocity")
	bodyVelocity.Velocity = Vector3.new(0, 0, 0)
	bodyVelocity.MaxForce = Vector3.new(9e9, 9e9, 9e9)
	bodyVelocity.Parent = humanoidRootPart

	local speed = 50

	flyConnection = runService.Heartbeat:Connect(function()
		bodyGyro.CFrame = workspace.CurrentCamera.CFrame
		bodyVelocity.Velocity = workspace.CurrentCamera.CFrame:VectorToWorldSpace(moveDir) * speed
	end)
end

local function stopFlying()
	if flyConnection then flyConnection:Disconnect() end
	if bodyGyro then bodyGyro:Destroy() end
	if bodyVelocity then bodyVelocity:Destroy() end
	moveDir = Vector3.zero
end

UIS.InputBegan:Connect(function(input, gpe)
	if gpe then return end
	if input.KeyCode == Enum.KeyCode.W then moveDir = Vector3.new(0, 0, -1) end
	if input.KeyCode == Enum.KeyCode.S then moveDir = Vector3.new(0, 0, 1) end
	if input.KeyCode == Enum.KeyCode.A then moveDir = Vector3.new(-1, 0, 0) end
	if input.KeyCode == Enum.KeyCode.D then moveDir = Vector3.new(1, 0, 0) end
	if input.KeyCode == Enum.KeyCode.Space then moveDir = Vector3.new(0, 1, 0) end
end)

UIS.InputEnded:Connect(function(input)
	if input.UserInputType == Enum.UserInputType.Keyboard then
		moveDir = Vector3.zero
	end
end)

button.MouseButton1Click:Connect(function()
	flying = not flying
	if flying then
		startFlying()
		button.Text = "Stop Flying"
	else
		stopFlying()
		button.Text = "Fly Mode"
	end
end)