I might be out of turn, but: As far as I’m aware the Outlook app for iPadOS isn’t really keen on playing nice with, well, anything; not Agenda or even Apple Notes.
Indeed, drag and drop may not work for all apps. It depends on each app putting useful info on the clipboard, and it is possible Outlook is not doing that.
If that is the case, there isn’t much we can do. You could make a request to Microsoft to improve it, but it is a big company, and difficult to move, if you know what I mean.