I am using your Renovation theme with Elementor page builder. All of the support I can find regarding the mega menu shows creating the mega menus with Visual Composer / WP Bakery. As far as I understood, when you were uploading a theme you had to choose between uploading tm-renovation-elementor or tm-renovation-wpb. How are you supposed to create mega menus if you chose to use elementor?
You can build mega menu via elementor by adding block and element normal: