I am trying to understand whether this is:

a Qt issue,

an OpenGL context / event loop issue, or

a NVIDIA driver leak (Threaded Optimization?).

When i disable Threaded Optimization in the nvidia settings , the leak dissappears.

class GLWidget : public QOpenGLWidget
{
    Q_OBJECT
public:
    explicit GLWidget(QWidget* parent = nullptr);
    void initializeGL() override;
    void paintGL() override;
    void resizeGL(int w, int h) override;

protected:
    void resizeEvent(QResizeEvent* event) override;

private:
    QTimer timer;
};

///////////////////////////////////////////////////////////////////////////////////////

GLWidget::GLWidget(QWidget* parent) : QOpenGLWidget(parent)
{
    QSurfaceFormat fmt;
    fmt.setSwapBehavior(QSurfaceFormat::DoubleBuffer);
    fmt.setProfile(QSurfaceFormat::CoreProfile);
    fmt.setVersion(4, 5);
    QSurfaceFormat::setDefaultFormat(fmt);

    connect(&timer, &QTimer::timeout, this, [this]() {
        update();
    });

    timer.setTimerType(Qt::PreciseTimer);
    timer.setInterval(0); // repaint as fast as possible
    timer.start();
}

void GLWidget::initializeGL()
{
    // nothing here
}

void GLWidget::resizeGL(int w, int h)
{
    glViewport(0, 0, w, h);
}

void GLWidget::paintGL()
{
    // EMPTY on purpose
    // glClearColor(0,0,0,1);
    // glClear(GL_COLOR_BUFFER_BIT);
}