angular ng e2e testcase with file download not working with headless chrome

In an angular2+ project I have an e2e testcase that clicks a button, a file gets downloaded, and the content is checked. It works in normal mode, but not in --headless mode. The file is not downloaded, and the testcase times out.

In my protractor.conf.js I already tried a lot of flags I found in different places:

const os = require('os');
[...]

  capabilities: {
    'browserName': 'chrome',
    chromeOptions: {
      args: ['--headless', '--disable-gpu', '--disable-popup-blocking', '--no-sandbox', '--window-size=1024,768', '--remote-debugging-port=9222', "--disable-dev-shm-usage"],
      prefs: {
        'download': {
          'prompt_for_download': false,
          'directory_upgrade': true,
          'default_directory': os.homedir() + '/Downloads'
        }, 
        safebrowsing: {enabled: false, disable_download_protection: true},
        browser: {set_download_behavior: { behavior: 'allow' }}
      }
    }
  },

Without success.

Also I read somewhere that you could configure it like this

// works for headless and "normal" mode
browser.driver.sendChromiumCommand('Page.setDownloadBehavior', {
    'behavior': 'allow',
    'downloadPath': DOWNLOAD_DIR
});

But there is no "sendChromiumCommand" in any "browser" variable, neither in the protractor.conf.js nor in the spec ts file.

How can I get this to work? Thanks in advance.