I identified a conflict between QtQuick.Controls and Felgo library. If I import both libraries Page QML Type of Felgo with the navigationBarHidden property is not used. The incompatibility of QtQuick.Controls with Felgo library is a critical issue for professional app development. I found a workaround by importing the Felgo library just in the main QML file file with functions. I noticed, that even QtQuick.Layouts is not part of the Felgo SDK.
it looks like you run into a namespace conflict here, which is easily solved. The missing navigationBarHidden property comes from the fact that you import QtQuickControls AFTER Felgo, thus the Page type from the controls module overrides the Felgo module. So you have 2 options:
import Felgo after controls, to give the Felgo components priority
import Felgo or controls as own namespace, e.g. like that: