Wouldn’t you wish that the VSTGUI uidescription test examples that come along with the VST3SDK would work ? Well, so would I.
But actually there is no problem if you were to use VSTGUI version 4.3, which came along with the VST3SDK version 3.66 and anything later does not work.
It appears that the examples are not being updated to work with respect to the constantly being updated VST3SDK and the VSTGUI itself.
What a pity given that it is not easy to obtain specific SDK’s.