Mega Menu

you do not need to pre define the place when a new row is started at mega menu!
you can do that by setting the mega div submenu to a grid layout:

https://kriesi.at/support/topic/tip-responsive-mega-div/

but:

I forgot to tell you that from the mobile phone, so I’m not talking …

You have a normal text menu on mobile phone? …
so it’s about the hamburger menu (a mega div with 7 columns next to each other on the cell phone is hardly recommendable)

next: images besides the menu-items text could be placed by doing it manually on label input field on menu page.
or look to the link – there is a way to have the featured images besides the menu-item link.

first : do not set on menu – that there should be a new row:

We do this by our css !

that would be new to me, that Enfold automatically sets a new row after 6 submenu items.

Then I’m sorry, because I see that a new submenu is set in the DOM every 6 menu items. I thought you did this manually.
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i see on Enfold code that there is a max_columns defined on class_megamenu.php and in helper-responsive-megamenu.php
maybe a filter could help here

Yes – that discussion is now from me to the devs or mods – and my hope is that it will find a solution then for you.
______________
we can have that filter :

function change_max_columns_on_mega_div($args){
  $args['max_columns'] = 7;
  return $args;
}
add_filter('wp_nav_menu_args', 'change_max_columns_on_mega_div', 10, 1);

but we had to find now a solution for the missing calculation of positioning the mega-div for that case

on a test installation i inserted the above snippet to child-theme functions.php:

function change_max_columns_on_mega_div($args){
  $args['max_columns'] = 7;
  return $args;
}
add_filter('wp_nav_menu_args', 'change_max_columns_on_mega_div', 10, 1);

and put in addition ( due to the lack of calculation for this case in Enfold avia.js ) in my quick css:

.avia_mega_div.avia_mega7 {
  right: calc(-100vw) !important;
  width: 95vw;
}

see example page on “Mega” Menu-Item : https://basis.webers-testseite.de/

do you use a child-theme ?

see here the documentation: https://kriesi.at/documentation/enfold/child-theme/

This is my recommended use of WordPress themes. You can easily change the settings of the parent theme – and these will be retained even after updates.

A child theme has on start ( you see the link above got a preset child-theme to download ) these three files : style.css / functions.php and a screenshot.png
in style.css there is the info of parent theme name and how to find the template
the functions.php is at start nearly empty ( editing that file : do not overwrite the first line )
the png is only to have a preview on themes overview.

A child theme is placed besides the parent theme