after some research, I was thinking of subclassing QAbstractTableModel and reimplement the data() function to suit my needs.

But I can't find any example on how to subclass QAbstractTableModel properly.

Then I could simply use MyTableModel in a tableview

This model will make the rows of the source model become columns of the proxy model and vice-versa.

Take a look at that, either to use directly or possibly to adapt to your case. The point being, the rows/columns are swapped/rotated at the model stage, for direct use in QTableView, rather than making the view have to deal with it.

I am using a C++ model like that

MyCppModel {
    id: myModel
    container: myCppContainer
}

with myCppContainer being something like that

class CppContainer : public QObject
{
public:
    CppContainer(QObject *parent=nullptr);

    // getter
    // setter

private:
    QVecto<MyElement*> m_elements;
}

and MyCppModel being like that

class MyCppModel : public QAbstractListModel
{
    Q_OBJECT
    Q_PROPERTY(CppContainer *container READ getContainer WRITE setContainer NOTIFY sigContainerChanged)
    Q_PROPERTY(int count READ count NOTIFY sigCountChanged)

public:
    explicit MyCppModel(QObject *parent = nullptr);

    enum {
        Role1 = Qt::UserRole
        Role2,
        Role3
    };

    // Basic functionality:
    int rowCount(const QModelIndex &parent = QModelIndex()) const override;

    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;

    virtual QHash<int, QByteArray> roleNames() const override;

    CppContainer *getContainer() const;
    void setContainer(CppContainer *container);

    Q_INVOKABLE QVariantMap get(int row);    
    int count() const;
signals:
    void sigContainerChanged();
    void sigCountChanged();
public slots:
    Q_INVOKABLE void refreshIndex(UInt32);
private:

    CppContainer *m_container;
};

Are you using a C++ model ? If so you can use a proxy that does that.