When I launch the Quick Look Preview Extension target in Xcode, an app called Quick Look Simulator opens with an almost empty window:
Online I read that the Terminal command qlmanage allows to test Quick Look plugins (which I think were an older format for creating Quick Look extensions), but running
qlmanage -p /path/to/previewed/file -c public.text -g /path/to/QuickLookPreviewExtension.appex
(where QuickLookPreviewExtension.appex is generated by the Xcode build and is located in the DerivedData folder) gives an error
Can't get generator at QuickLookPreviewExtension.appex
How can I debug a Quick Look Preview Extension?