Attached Outlook items not retained in Office 365 Group Calendar meeting or appointment
Original KB number: 4499943
When you use Outlook for Office 365, Outlook 2019, or Outlook 2016 to attach an Outlook item to an Office 365 Modern Group Calendar appointment or meeting, the attachment isn't retained.
This issue occurs when using the Outlook Item button on the Insert tab of the ribbon. This is a known limitation in Outlook with Office 365 group calendars.
Copy and paste the contents of the wanted Outlook item into the body of the meeting or appointment. Alternatively, you can upload the Outlook item to Files in the Office 365 Group or to OneDrive for Business and then include a link in the body of the meeting or appointment.