Qt 6 is a major version, and migrating a real Qt 5 application to it is more than a recompile. The framework was modularised, the build system shifted toward CMake, some APIs were removed or replaced, and modules moved around. None of it is insurmountable, but a successful migration is planned,...
Source: [Dev.to](https://dev.to/mecanik-dev/qt-5-to-qt-6-migration-guide-for-2026-30g0)