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)
Gerhard Schwanzer