Unable to attach instant file link in Outlook

One of the users that I support has been having problems with his Outlook and being able to use the Document cloud Add-in that comes with the Acrobat installation. At this KB link, it shows the behaviour that he wants https://helpx.adobe.com/uk/acrobat/using/adobe-document-cloud-for-outlook.html however, this button does not appear when composing new messages. When he attaches PDFs normally, he also doesn't get the prompt to change to using a link.

He gets the Acrobat tab that allows attaching as PDF and the settings button, just not the ability to send as a link directly in Outlook.

I have tried reinstalling Acrobat, Office, removing and re-adding the add-in directly within Outlook from the options. Always send files as a link is ticked in Acrobat preferences.

He is using Outlook 365 semi annual channel.