How to get rid of unwanted rounded squares (checkboxes) in QTableView items?

I have a QTableView with some data (numbers), but each cell contains an unwanted rounded square (maybe a non-functional checkbox). They look bad, occupy space, and can obscure my data.

Why do they appear? How can I remove them?

#include <QtWidgets/QApplication>
#include <QtWidgets/QMainWindow>
#include <QTableView>
#include <QHeaderView>

class MyModel : public QAbstractTableModel
{
public:
    int rowCount(const QModelIndex& index) const override {return 5;}
    int columnCount(const QModelIndex& index) const override {return 2;}
    QVariant data(const QModelIndex& index, int role) const override
    {
        if (role == Qt::DisplayRole)
            return 3000 + index.row() * 100 + index.column();
        else
            return 0;
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMainWindow w;
    QTableView widget;
    MyModel model;
    widget.setModel(&model);
    widget.horizontalHeader()->hide();
    widget.verticalHeader()->hide();
    w.setCentralWidget(&widget);
    w.show();
    return a.exec();
}

I use Qt 6.8.0 on Windows 11.

The QAbstractItemModel::data() documentation states:

Note: If you do not have a value to return, return an invalid (default-constructed) QVariant.

There are many roles defined, but you are only looking for Qt::DisplayRole and then you are returning 0 for all the rest. Chances are, you are being queried for Qt::CheckStateRole and thus returning a "false" checked state for it, which would explain why the check boxes appear.

Roles describing appearance and meta data (with associated types):

Constant	Value	Description
...	...	...
Qt::CheckStateRole	10	This role is used to obtain the checked state of an item. (Qt::CheckState)
...	...	...

So, do what the documentation says - return an empty QVariant instead:

QVariant data(const QModelIndex& index, int role) const override
{
    if (role == Qt::DisplayRole)
        return 3000 + index.row() * 100 + index.column();
    else
        // return 0;
        return QVariant(); // <-- HERE
}