As a Roblox developer, having the documentation and function of TopbarTransparencyChangedSignal is inconvenient on the platform and typing when using PlayerGui with topbar purposes, as the property itself isn’t useable.
Confirmed by Roblox that TopBar would be removed, the code for this is still available to use yet it should be marked deprecated and removed from the Engine and documentation.
There’s no tag or warning that this isn’t deprecated and shouldn’t work onto the Roblox Engine itself, the function itself doesn’t even work as intended.