Correct InputMethod for QtQuick.VirtualKeyboard / qtvirtualkeyboard

[Predot]

Hello, I want to use the QtQuick.VirtualKeyboard. When I use it in the following way, I can use all features of the virtual keyboard:

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.VirtualKeyboard 2.15

Window {
    id: window
    width: 640
    height: 480
    visible: true

    TextEdit {
        id: textEdit
        height: 30
        anchors.fill: parent
    }

    InputPanel {
        id: inputPanel
        z: 99
        anchors.left: parent.left
        anchors.right: parent.right
        anchors.bottom: parent.bottom
        width: window.width
    }
}

But I want to write a custom input method, like described here: https://doc.qt.io/qt-6/technical-guide.html#implementing-a-custom-input-method
I tried to implement this in the following way:

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.VirtualKeyboard 2.15

Window {
    id: window
    width: 640
    height: 480
    visible: true

    TextEdit {
        id: textEdit
        height: 30
        anchors.fill: parent
        enabled: false
    }

    InputPanel {
        id: inputPanel
        z: 99
        anchors.left: parent.left
        anchors.right: parent.right
        anchors.bottom: parent.bottom
        width: window.width
    }

    InputMethod {
        id: customInputMethod

        function inputModes(locale) {
            return [InputEngine.Cyrillic, InputEngine.Latin, InputEngine.Numeric];
        }
        function selectionLists() {
            return [];
        }

        function setInputMode(locale, inputMode) {
            return true
        }

        function setTextCase(textCase) {
            return true
        }

        function reset() {
            // TODO: reset the input method without modifying input context
        }

        function update() {
            // TODO: commit current state and update the input method
        }

        function keyEvent(key, text, modifiers) {
            var accept = true
            textEdit.text = text
            return accept;
        }
    }

    Component.onCompleted: {
        InputContext.inputEngine.inputMethod = customInputMethod
    }
}

But compared with the built-in input method, the virtual keyboard has now only a subset of the features. Most important for me is, that the shift key is not working, means i can only write lower case letters. Has somebody an idea to enable the shift key?

I guess it could be solved by setting InputContext.inputMethodHints to something unequal zero, but this property is readonly. Is there a way to manipulate this property without using a text input field (the problem is that I would have to struggle with the focus of this text input field, and I dont need a text input).

When I debug the first code snipped I can observe that InputContext.inputEngine.inputMethod has the value PlainInputMethod, but I can not find this input method as qml type (to override the keyEvent() method for my purposes).