MenuBar {
        Menu {
            title: qsTr("&File")
            MenuItem {
                text: qsTr("E&xit")
            }
        }
        Menu {
            title: qsTr("&Edit")
        }
        Menu {
            title: qsTr("&Help")
            MenuItem {
                text: qsTr("About...")
            }
        }
    }

Of course I can set the height of the MenuItem manually but it doesn't work correctly for MenuBar (only the background has smaller size) and I think it's not the good approach.

Other examples without OpenGL handling but with MenuBar usage in qml have normal height. Also it doesn't have separate styles or size adjustments - for example Qt Quick Controls - UI Forms - https://doc-snapshots.qt.io/qt5-5.11/qtquickcontrols-uiforms-example.html