flutter - Flutter Matrix Chat - E2E Encryption not working with Famedly Matrix SDK

Question

I used the Famedly Matrix SDK to create a Flutter Chat app. Here I would like to integrate end to end encyrption, but I can't get it to work. I have created a minimal app for testing. Below is the source code. Sending unencrypted messages is working as expected. I also can create encrypted rooms and send messages to it, but they all appear unencrypted in the romm.

Encryption in general is working with an JavaScript version I've written with the official JS SDK and React.

Maybe someone of you will notice what is missing here.

pubspec.yml

name: chat_app
description: A new Flutter project.

publish_to: "none" # Remove this line if you wish to publish to pub.dev
version: 1.0.0+1

environment:
  sdk: ">=2.12.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  flutter_olm: ^1.1.2
  flutter_openssl_crypto: ^0.0.1
  cupertino_icons: ^1.0.2
  matrix_api_lite: ^0.3.3
  matrix: ^0.1.5
  moor: 4.3.2
  database: ^0.3.3

dev_dependencies:
  flutter_test:
    sdk: flutter

flutter:
  uses-material-design: true

main.dart

import 'package:flutter/material.dart';
import 'package:matrix/encryption.dart';
import 'package:matrix/matrix.dart';

Client? client;

void main() {
  client = Client("HappyChat",
      enableE2eeRecovery: true,
      verificationMethods: {KeyVerificationMethod.numbers},
      supportedLoginTypes: {AuthenticationTypes.password});

  if (client == null) {
    throw ('The client is not initialized');
  }

  var uri = Uri.parse("http://192.168.178.20:8008");
  client!.homeserver = uri;

  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  String _title = 'My Title';
  final roomId = '!RezBsiFvjPJAMnpYpc:cloudbucket1.matrix.host';
  Room? _room;

  _MyHomePageState() {
    this._title = "CONNECTING";
  }

  Future<void> loginClient() async {
    try {
      await client!.login(
          identifier: AuthenticationUserIdentifier(user: 'ppulwey'),
          password: 'MyPassword');

      print("Client supports encryption ${client!.encryptionEnabled}"); //* This is always false!!!

      this._room = client!.getRoomById(roomId);
      if (this._room == null) {
        throw ('Room not found');
      }

      print("Room is ${this._room!.encrypted ? "already" : "not"} encrypted");

      if (!this._room!.encrypted) {
        this._room!.enableEncryption();
      }

      final joinedRooms = await client!.getJoinedRooms();

      if (!joinedRooms.contains(this.roomId)) {
        this._room!.join();
      }
    } catch (e) {
      print(e);
    }
  }

  Future<void> sendMessage() async {
    try {
       // * Also tried this
      // var eventContent = Map<String, dynamic>();
      // eventContent['body'] = 'Hallo du Äffchen';
      //eventContent['msgtype'] = MessageTypes.Text;
      //_room!.sendEvent(eventContent, type: 'm.room.message');

      _room!.sendTextEvent('Encrypted now');
    } catch (e) {
      setState(() {
        _title = 'FAIL';
      });
      print(e);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(_title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
            ElevatedButton(
                onPressed: loginClient, child: const Text('Initialize'))
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: sendMessage,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}