The QUnixOSVersion fallback list is wrong
Current list: /etc/os-release /etc/lsb-release /etc/redhat-release /etc/debian_version
Right list: /etc/os-release /usr/lib/os-release /etc/lsb-release /etc/redhat-release /etc/debian_version

"The file /etc/os-release takes precedence over /usr/lib/os-release. Applications should check for the former, and exclusively use its data if it exists, and only fall back to /usr/lib/os-release if it is missing. Applications should not read data from both files at the same time. /usr/lib/os-release is the recommended place to store OS release information as part of vendor trees. /etc/os-release should be a relative symlink to /usr/lib/os-release, to provide compatibility with applications only looking at /etc. A relative symlink instead of an absolute symlink is necessary to avoid breaking the link in a chroot or initrd environment such as dracut."

References: https://www.freedesktop.org/software/systemd/man/os-release.html