a) using a system provided KF6
b) downloading and compiling KF6
c) using the vendored-in re-creation of the functionality
The behaviour for both Qt5 and Qt6 is steered with the same two variables which were renamed to become version agnostic:
a) BUILD_WITH_KF=ON BUILD_KF=OFF
b) BUILD_WITH_KF=ON BUILD_KF=ON
c) BUILD_WITH_KF=OFF
The version is automatically derived from the chosen Qt major version.
The BUILD_WITH_KF5 option was checked with DEFINED, so passing -DBUILD_WITH_KF5=OFF still entered the KF5 setup path.
Skip the KF5 setup when disabled and provide small Qt-only replacements for the KDE color widgets used by .ui files in that build mode.
Assisted-by: pi coding agent / Mika (OpenAI GPT-5.5)