StudioTheme contains a method called GetPath(). This method is missing various pieces of documentation including the assetid strings, but that’s outside the scope of this bug report.
The main issue is, the function returns a blank string, for everything.
I am even yet to find an FFlag that may be causing this to not work as intended.
This seems to be a problem with the documentation, rather than Studio. I can confirm that this method does return real paths for valid names - however it seems that at some point “MoreButton” ceased to be a valid path.