"Crop dialog" in the help does not exist
in the GIMP online help document in part II, chapter 10 par. 1.2.2: Cropping it says: ... With the tool active, clicking and dragging in the image will sweep out a crop rectangle. It will also pop up a dialog that allows you to adjust the dimensions of the crop region if they aren't quite right. When everything is perfect, hit the Crop button in the dialog.
But there is no Crop dialog (any more?). You have to use the Tool options and you have to hit the Enter button in the end.