This is not supported. Right now, each object can only be open in one place at a time.

The side panel can show objects, but it cannot show a second copy of the same page or a specific block from that page. That’s why opening a page in the side panel and then choosing Open as page removes it from the side panel again.

If you want an outline on one side and a draft on the other, a good workaround is:

• Create a separate page (for example, just for your outline or notes).
• Open your main page in the main area.
• Open the outline page in the side panel.
• When you are done, copy the content back into the main page and delete the temporary page if you like.

If you would like this to change, you can upvote or comment on the open request “Allow the same object to be opened in the side panel”.