Hello Limor1,
Good day! Hope this finds you well.
In the new outlook, you can double left click on the email from the list to open in a new tab. If you need to add it to the quick actions to appear beside sender names and subject lines in your message list, in the reading pane, click on more actions ... >Customize actions >check the option to open in a new window in the customize reading pane actions.
In case you have any further queries, please let me know.
Best Regards,
Ashraf.