Mega Menu for Genesis Themes using CSS - https://amethystwebsitedesign.com/mega-menu-for-genesis-themes-using-css

functions.php

<?php // Do not add this line

// Reduce the primary navigation menu to two levels depth.
add_filter( 'wp_nav_menu_args', 'genesis_sample_primary_menu_args' );
function genesis_sample_primary_menu_args( $args ) {

	if ( 'primary' != $args['theme_location'] ) {
		return $args;
	}

	$args['depth'] = 2;

	return $args;
}

style.css

/* Already in genesis sample theme */
.genesis-nav-menu .sub-menu .sub-menu {
	margin: -56px 0 0 199px;
}

/* Add the following below it */
.genesis-nav-menu .megamenu .sub-menu {
	background-color: #fff; /* same color as .genesis-nav-menu .sub-menu a */
	border: 1px solid #eee; /* optional, if a border is desired */
	height: auto;
	width: 610px; /* make width needed plus 10px */
	column-count: 3; /* optional to change the order of the items to be vertical */
	column-gap: 0; /* optional to change the order of the items to be vertical */
}

.genesis-nav-menu .megamenu.move .sub-menu {
	right: 0;
} /* optional to right align the sub-menu */

.genesis-nav-menu .megamenu .sub-menu a {
	border: 0; /* optional */
	width: 200px; /* 1/3 width for 3 columns */
	/* width: 300px; /* 1/2 width for 2 columns */
}

/* Mobile Menu
This is not needed for mobile-first themes - see blog post for this.
Find section @media only screen and (max-width: 1023px) {
In that section find, already in genesis sample theme
*/
	.js .genesis-nav-menu .sub-menu .sub-menu {
		margin: 0;
	}

/* Add the following below it */
	.genesis-nav-menu .megamenu .sub-menu {
			column-count: 0; /* optional if added above */
                        overflow: hidden;
			width: 100%;
	}

	.genesis-nav-menu .megamenu .sub-menu a {
		width: auto;
	}