cp /usr/lib/x86_64-linux-gnu/qt5/plugins/platforminputcontexts/libfcitxplatforminputcontextplugin.so /opt/Qt5.14.2/Tools/QtCreator/lib/Qt/plugins/platforminputcontexts/libfcitxplatforminputcontextplugin.so
Copy this file to the installation directory.
Plus permissions:
chmod +x libfcitxplatforminputcontextplugin.so
Just restart Qt Creator.
Qt creator editing and application in ubuntu system use Chinese input method