UIAspectRatioConstraint Plugin

local selection = game:GetService("Selection")

local toolbar = plugin:CreateToolbar("UIAspectRatio")

local pluginButton = toolbar:CreateButton(
    "Create",
    "",
    "rbxassetid://89279974687939"
)

pluginButton.ClickableWhenViewportHidden = true

pluginButton.Click:Connect(function()

    for _, object in pairs(selection:Get()) do

        if object:IsA("GuiObject") then
            local uiarc = object:FindFirstChildOfClass("UIAspectRatioConstraint") or Instance.new("UIAspectRatioConstraint")
            uiarc.AspectRatio = object.AbsoluteSize.X / object.AbsoluteSize.Y
            uiarc.Parent = object
        end
    end

    pluginButton:SetActive(true)
    pluginButton:SetActive(false)
end)