How to create a root level folder in Chrome bookmarks

Solution 1:

The three top folder are not real folders, they are telling you how their content is treated (displayed/not displayed/only displayed on mobile devices).
That is a fixed list and cannot be extended.

Any folders you add would be either visible in the bookmark bar, or not visible, right? (Or visible only on mobile). So they will be shown inside the respective lists.

Solution 2:

If you alter your definition of "top level", you can get a new folder in the top level of the Bookmarks folder.

It is worth mentioning this because if you don't use the Bookmarks toolbar, adding a folder to the Bookmarks Bar adds the folder to the top level of the Bookmarks menu, which is as top-level as it gets.

Details:

Bookmarks > Bookmark Manager > Select Bookmarks Bar > Click the "..." menu for Bookmarks (not the "..." menu for an individual folder) > "Add new folder"