QML, the menu icon will does not show up correctly

The following standard QML code does not work. Instead of the 3 small bar menu icon (unicode u2630), I get a rectangle with a cross inside: it does not find the character. However it finds the u25C0 left arrow (back triangle button) when required.

This is only a cosmetic glitch, as it works perfectly.

Has this anything related to the font, or with a mapping to an icon? How to solve this?

import QtQuick 2.15
import QtQuick.Controls 2.15

ApplicationWindow {
    id: window
    width: 640
    height: 480
    visible: true
    title: qsTr("Stack")

    header: ToolBar {
        contentHeight: toolButton.implicitHeight

        ToolButton {
            id: toolButton
            text: stackView.depth > 1 ? "\u25C0" : "\u2630"
            font.pixelSize: Qt.application.font.pixelSize * 1.6
            onClicked: {
                if (stackView.depth > 1) {
                    stackView.pop()
                } else {
                    drawer.open()
                }
            }
        }

        Label {
            text: stackView.currentItem.title
            anchors.centerIn: parent
        }
    }
(...)