Hi!
This issue will be fixed along with the next Qt version upgrade for Felgo from Qt 6.4.3 to Qt 6.6 or higher. This will be with Felgo 4.3.0 in the second quarter of 2024.
Until this release, you can very easily add the fix for this qmake issue to your local Felgo installation. To do so, open the mkspecs/features/toolchain.prf of the Build Kit folder in your Felgo installation. Then apply the changes shown in the diff here: https://codereview.qt-project.org/c/qt/qtbase/+/503172/3/mkspecs/features/toolchain.prf
Hope this helps!
Best,
Günther