On Chrome it now works. But on Opera still not: Failed to execute ‘postMessage’ on ‘DOMWindow’: The target origin provided (‘https://www.youtube.com’) does not match the recipient window’s origin (‘https://www.wix.com’).
errors.js:333 Uncaught (in promise) Error: WDE0053: Internal wixData error: WDE0054: The server could not fulfill the request.
On Edge same postmessage-error, but no WDE0053/0054 error.
Might be an Opera thing: I have had some trouble with postMessage too on latest releases of Opera.