Yes, I can confirm this issue as well on Qt 6.9.3 and MacOS 15.6.1
When passing QFileDialog::DontUseNativeDialog for options parameters the dialog shows correctly, e.g.:
QString fileName = QFileDialog::getOpenFileName(this, tr("Open File"), lastOpenDir, tr("Images (*.png *.bmp *.jpg *.tif *.gif)"), nullptr, QFileDialog::DontUseNativeDialog);
Note that this is a pointer to the QMainWindow of the application.
However I found this related bug report: QTBUG-135882
It has been closed, but when reading through the comments, apparently the solution is to replace add_executable with qt_add_executable in the CMakeLists.txt.
I tried this and it works for me. No need to pass the QFileDialog::DontUseNativeDialog parameter anymore and it will show the native MacOS dialog correctly.