Some APIs are marked as deprecated on the documentation for GuiObject, but they haven’t been marked as deprecated in Studio (both in the object browser and in the script editor).
This causes Luau to not emit warnings for using them, which has tricked me into using the tweening functions for over a year without knowing that they were deprecated.
Affected APIs
Properties:
GuiObject.TransparencyGuiObject.BorderColor
Methods:
GuiObject:TweenPosition()GuiObject:TweenSize()GuiObject:TweenSizeAndPosition()
(side note: GuiObject isn’t shown in the object browser, which has been reported before for other classes and has gone unresolved for years)
Relevant documentation: GuiObject | Documentation - Roblox Creator Hub