The problem is that the TypoScript cObjects normally return a rendered (as configured) representation (a string). In Fluid you iterate through objects or arrays. Therefore TypoScript und Fluid don't work together the way you'd like.
Have a look at the extension "vhs". It brings you the features you need, e.g. for a menu: https://fedext.net/viewhelpers/vhs/master/Page/MenuViewHelper.html
With vhs you no longer need to define menus in TypoScript.