Dear Greg Borrageiro;
Thank you for reaching out to Microsoft customer support. I understand that you are experiencing an issue with the "Insert as Text" option missing from the "Insert Attachment" option when composing an email in Outlook for Windows - For business.
I apologize for the inconvenience this may have caused you. The "Insert as Text" option is not available when inserting an HTML attachment in Outlook for Windows - For business. This is because HTML attachments are designed to be viewed as a separate file, rather than being embedded in the body of the email.
However, you can still insert the HTML code into the body of the email by following the steps in the article you provided. Please note that this will not embed the HTML file as an attachment, but rather insert the code into the body of the email.
If you have any further questions or concerns, please do not hesitate to reach out to us.
We look forward to hearing from you, please let me know and provide a more detailed description so we can provide you with more specific assistance. Thank you for your cooperation.
Sincerely,
De Paul | Microsoft Community Moderator