How can I lockdown a Flutter App to Kiosk App?

Question

I recently started to move an Android App to Flutter. I enjoy the way Flutter Apps are coded. After 2 days the Flutter App had the same functionality as the Android App. The only feature missing is the lockdown. The Android App is running on coperate owned devices and is device owner. The lockdown is achieved by the following methods:

    private void setDefaultCosuPolicies(boolean active) {
    // set user restrictions
    setUserRestriction(UserManager.DISALLOW_SAFE_BOOT, active);
    setUserRestriction(UserManager.DISALLOW_FACTORY_RESET, active);
    setUserRestriction(UserManager.DISALLOW_ADD_USER, active);
    setUserRestriction(UserManager.DISALLOW_MOUNT_PHYSICAL_MEDIA, active);
    setUserRestriction(UserManager.DISALLOW_ADJUST_VOLUME, active);

    // disable keyguard and status bar
    mDevicePolicyManager.setKeyguardDisabled(mAdminName, active);
    mDevicePolicyManager.setStatusBarDisabled(mAdminName, active);

    // enable STAY_ON_WHILE_PLUGGED_IN
    enableStayOnWhilePluggedIn(false);

    // set this Activity as a lock task package

    mDevicePolicyManager.setLockTaskPackages(mAdminName,
            active ? new String[]{getPackageName()} : new String[]{});

    IntentFilter intentFilter = new IntentFilter(Intent.ACTION_MAIN);
    intentFilter.addCategory(Intent.CATEGORY_HOME);
    intentFilter.addCategory(Intent.CATEGORY_DEFAULT);

    if (active) {
      // set Cosu activity as home intent receiver so that it is started
      // on reboot
      mDevicePolicyManager.addPersistentPreferredActivity(
              mAdminName, intentFilter, new ComponentName(
                      getPackageName(), MainActivity.class.getName()));
    } else {
      mDevicePolicyManager.clearPackagePersistentPreferredActivities(
              mAdminName, getPackageName());
    }
  }

  private void setUserRestriction(String restriction, boolean disallow) {
    if (disallow) {
      mDevicePolicyManager.addUserRestriction(mAdminName,
              restriction);
    } else {
      mDevicePolicyManager.clearUserRestriction(mAdminName,
              restriction);
    }
  }

  private void enableStayOnWhilePluggedIn(boolean enabled) {
    if (enabled) {
      mDevicePolicyManager.setGlobalSetting(
              mAdminName,
              Settings.Global.STAY_ON_WHILE_PLUGGED_IN,
              Battery_PLUGGED_ANY);
    } else {
      mDevicePolicyManager.setGlobalSetting(
              mAdminName,
              Settings.Global.STAY_ON_WHILE_PLUGGED_IN, DONT_STAY_ON);
    }
  }

In the MainActivitys onCreate function setDefaultCosuPolicies(true) was called. I copied these functions to the flutter app. Added the AdminReceiver and configured everything in the AndroidManifest. The first attempt didn't work so I tried to call the setDefaultCosuPolicies function through a MethodChannel. This also did not work.

Does anyone have any idea how to activate the kiosk functionality?

Thanks in advance