Using New Outlook on Windows for professional communication and productivity
I had the same problem and think the "New" program is not great.
However, you can still use copy paste if you use the keyboard shortcut commands of "control C" (copy) "control V" (Paste).
So you select the file in the folder (or multiple files) hit the "control" key and "C" key at the same time, then go to you remail in the body message area and click the left mouse button, so the curser is flashing there. Then hit the "control" key and "V" key on the keyboard at the same time.