Using classic Outlook for Windows in educational settings
I woke up today with this exact same problem. It looks like an update was done to Outlook over the weekend as now I see a couple things have moved and I have a calendar showing 2 months instead of 1 (little things), but this is a giant pain! As now I cannot use arrow keys or ctrl+c on any cell in an excel preview file. exactly as OP says. I spend most of my work day opening emails with excel attacments and highlighting and selecting data to paste elsewhere. I'm following this to hopefully find some sort of solution to not completely destroy my workload.