Have the same issue, did a lot of research, as of now, there are no solutions.
How to live with this problem:
- It looks like this is a bad "How to use" explanation...
- Probably, the Team responsible for this UI/UX imagined that we would click the "select box" when trying to select an e-mail.
- By clicking in the selection box you don't open the email, just select it.
- You can get used to placing your click on this selection to avoid "Single Click Open"
This is the second time I give "New Outlook" a try and decide to back to old outlook due to the lack of basic features / settings. I recommend the same + give a feedback to Microsoft.