In a CMakeLists.txt, a standard name for a Qt component is like Qt6::Core or Qt5::Core. But we should see some projects' CMakeLists.txt contains like Qt::Core, it's a technology for generalization. However, the Qt where we can use this technic must be above Qt 5.15!
refer to:
https://doc.qt.io/qt-6/cmake-qt5-and-qt6-compatibility.html