negativeTabView->findChild<QSurfaceDataProxy *>("proxyTest");

Where 'negativeTabView' is a QQuickView object, and 'proxyTest' is the ItemModelSurfaceDataProxy from a Surface3DSeries in QML, like this:

Surface3DSeries {
                id: surfaceSeries
                flatShadingEnabled: false
                drawMode: Surface3DSeries.DrawSurface
                baseGradient: surfaceGradient
                colorStyle: Theme3D.ColorStyleRangeGradient
                itemLabelFormat: "(@xLabel, @zLabel): @yLabel"
                onSelectedPointChanged: getSurfaceDataItem(itemLabel, selectedPoint)


                ItemModelSurfaceDataProxy {
                    id:surfaceSeriesDataProxy
                    objectName: proxyTest
                    itemModel: surfaceData0.model
                    rowRole: "radius"
                    columnRole: "angle"
                    yPosRole: "value"
                }
            }

I cannot share my full code, but in my main.h I have included QSurfaceDataProxy, added the namespace, and added one QSurfaceDataProxy object in the private section, as such:

#include <QtDataVisualization/QSurfaceDataProxy>
using namespace QtDataVisualization;
...
 QSurfaceDataProxy *m_dataProxy;

In my main.cpp I have done included the same line

#include <QtDataVisualization/QSurfaceDataProxy>

without the namespace. If I try to instantiate the m_dataproxy variable like such:

 m_dataProxy = new QSurfaceDataProxy();

or

 m_dataProxy = negativeTabView->findChild<QSurfaceDataProxy *>("proxyTest");

It will lead to this error (full path removed)

C:\\....main.cpp:-1: error: undefined reference to `__imp__ZN19QtDataVisualization17QSurfaceDataProxyC1EP7QObject'

What am I doing wrong?
Here is the top of my .pro file:

QT       += core gui charts quickwidgets qml quick

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets printsupport

CONFIG += c++11

What am I doing wrong?
Using https://doc.qt.io/qt-5.9/qtdatavisualization-surface-surfacegraph-h.html as reference, they seem to instantiate their QSurfaceDataProxy in the same manner with no issues.

Thank you.