Mega Menu?

Mega Menu seems to only work with those themes that specifically take advantage of it.

Try using their Scratch theme as an example:

https://github.com/ThemeFuse/Scratch-Theme

The Styling and MegaMenu extensions are visible only when added to

// file: {theme}/framework-customizations/theme/manifest.php

$manifest['supported_extensions'] = array(
    'styling' => array(),
);

https://github.com/ThemeFuse/Scratch-Theme/blob/f7c08ab349635ef40dd8b1c88391f4d5bf22b4c4/scratch-parent/framework-customizations/theme/manifest.php#L12

because those extensions has no sense if the theme is not configured to display them correctly.

Sorry for late reply