Why can't I add attachments to emails using Windows Exchange and Windows 10?

[Windows Central Question]

Why can't I add attachments to emails using Windows Exchange and Windows 10

Accessing Windows Exchange (Oxford University Nexus) via Edge, clicking on the Add Attachments icon has no effect so that I cannot add attachments to an ongoing email. I can read attachments on incoming emails. It worked yesterday before upgrading from Windows 8.1 to 10