Hello,
The reported issue concerning YouTube video downloads has been successfully resolved.
Kindly attempt the download once more and confirm if the operation is successful.
If the issue persists, please collect a technical report (click the Parallels Toolbox icon in Mac menu bar > Settings (asterisk icon) > Help > Send Technical Data > check "Attach screenshots..." > press Send Report) and send the report's 9-digit ID in a reply to this post.
Thanks