Porting from Qt 5 into Qt 6
Qt 6 is a major change to the Qt framework, therefore it breaks some of the backward compatibility. So, before upgrading to Qt 6, make sure that your Qt 5 application is updated to Qt 5.15. Porting will be easier from Qt 5.15 to Qt 6, with the fewest number of changes. However, APIs marked as deprecated or obsolete in Qt 5.15 may have been removed from Qt 6.0.
The CMake APIs in Qt 5 and Qt 6 are almost identical in terms of semantics. As a result, Qt 5.15 introduced versionless targets and commands, allowing CMake code to be written that is completely independent of Qt versions. Versionless imported targets are most useful for projects that require both Qt 5 and Qt 6 compilation. It is not recommended to use them by default because of the missing target properties. You can read more on this at the following link: https://doc.qt.io/qt-6/cmake-qt5-and-qt6-compatibility.html.
Some of the classes and modules have been removed in Qt 6, but these are kept...
