The compilation fails with:

clang: error: no such file or directory: '/Volumes/MacDev/dev/qt/sensorbuilds-ios-cmake/grue/plugin/Debug/libqtsensors_grue.a'

The grue plugin path is not what the xcode project expects during linking.

The lib can be found in:
grue/plugin/Debug-iphoneos

in my build.

Built with:

qt-cmake /Users/tamasmartinec/dev/qt/git/6/qt5/qtsensors/examples/sensors/grue/ -GXcode

then opening the generated xcode project and running it.