USE_QT5 and ENABLE_GUI are (not) duplicates

We seem have a duplicate: USE_QT5 and ENABLE_GUI. This seems to be in conflict with !662 (merged).
Maybe we should sort alphabetically these ENABLE_* in this place where you edited them? Done in !731 (merged)

EDIT: USE_QT5 is our internal cmake flag. Not used by users. Soon we will have USE_QT6 #279.

Edited Jun 24, 2022 by Janek Kozicki