Using older versions of Outlook for Mac for personal email and calendar
I am using Outlook 16.74.1 (a recent update about a week ago). I too am now getting messages back from people "you didn't include the attachment" when I know I did. I am using the attach, and browsing from my hard drive.
I also can no longer go from office products and click "share" > (send Presentation / Sheet / Doc).
Very frustrating.