I can confirm that this behaviour is still present on kde 5.20.4. You can run e.g. khelpcenter and observe:
kf.service.services: The desktop entry file "/usr/share/applications/qemu.desktop" has Type= "Application" but no Exec line kf.service.sycoca: Invalid Service : "/usr/share/applications/qemu.desktop" -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1868221 Title: /usr/share/applications/qemu.desktop should have an "Exec=" key. Status in QEMU: New Bug description: According to the www.freedesktop.org .desktop-file specification, all "Application" desktop files should have an "Exec=" key. The one in qemu doesn't. This can be easily verified by running kbuildsycoca4 if KDE4 is present, but the issue is not DE-dependent. Which binary exactly should be assigned as the default one, I don't know. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1868221/+subscriptions