I have Qt6 installed system-wide (/usr/bin/qmake6, /usr/lib/qt6/) via the system package manager.

Trying to use the "Open Qt Widgets Designer" action:

No Qt installations root found. Please set an Qt installation root.

I tried to set it to either /, /usr/bin, /usr/lib, /usr/lib/qt6

None of them worked (Cannot find a Qt installation in "/usr/lib/qt6").

It should be noted that I can still get the designer to open if I open a UI file in the project, but the Open Qt Widgets Designer action seems to use a different system.

    "qt-core.additionalQtPaths": [
        {
            "name": "Qt-6.9.1-linux-g++",
            "path": "/usr/bin/qmake6"
        },
        {
            "name": "Qt-5.15.17-linux-g++_from_PATH",
            "path": "/usr/bin/qtpaths"
        }
    ],