FontLoader does not support loading font from resource file in iOS:
"This plugin does not support application fonts
qrc:/qml/gallery.qml:184:5: QML FontLoader: Cannot load font: "qrc:/fonts/OpenSans-Regular.ttf""

As a workaround you can use:

    FontLoader {
        id: myFont
        Component.onCompleted: {
            if (Qt.platform.os === "ios")
                name = "My Font"
            else
                source = "qrc:/fonts/MyFont-Regular.ttf"
        }
     }
    }

And load "My Font" using the workaround described in QTBUG-34490