/*!
Theme Name: Kadence Child
Theme URI: https://www.kadencewp.com/kadence-theme/
Template: kadence
Author: Kadence WP
Author URI: https://www.kadencewp.com/
Description: A child theme for the Kadence Theme.
Version: 1.0.0
License: GNU General Public License v3.0 (or later)
License URI: https://www.gnu.org/licenses/gpl-3.0.html
Text Domain: kadence-child
*/

/* Theme customization starts here
-------------------------------------------------------------- */

html {
	--hl-width: 0px;
}
.hl {
    padding-bottom: 5px !important;
    position: relative;
}

.mx-auto {
	margin-left: auto;
	margin-right: auto;
}

.hl::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: var(--hl-width);
    height: 5px;
    background-color: var(--global-palette2);
}
Here's the updated CSS that prevents the animation from working on sub-menu links:
css/*!
Theme Name: Kadence Child
Theme URI: https://www.kadencewp.com/kadence-theme/
Template: kadence
Author: Kadence WP
Author URI: https://www.kadencewp.com/
Description: A child theme for the Kadence Theme.
Version: 1.0.0
License: GNU General Public License v3.0 (or later)
License URI: https://www.gnu.org/licenses/gpl-3.0.html
Text Domain: kadence-child
*/
/* Theme customization starts here
-------------------------------------------------------------- */
html {
	--hl-width: 0px;
}
.hl {
    padding-bottom: 5px !important;
    position: relative;
}
.mx-auto {
	margin-left: auto;
	margin-right: auto;
}
.hl::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: var(--hl-width);
    height: 5px;
    background-color: var(--global-palette2);
}
/* Only apply animation to top-level menu items - accounting for the wrapper div */
.kb-navigation > .wp-block-kadence-navigation-link > .kb-link-wrap > a {
    position: relative;
}
.kb-navigation > .wp-block-kadence-navigation-link > .kb-link-wrap > a:hover {
	color: var(--global-palette9) !important;
}
.kb-navigation > .wp-block-kadence-navigation-link > .kb-link-wrap > a::before {
    content: '';
    position: absolute;
    top: 50%;
	transform: translateY(-50%);
    left: 0;
    width: 0;
    height: 70%;
    transition: all linear 120ms;
    background-color: var(--global-palette2);
	z-index: -1;
}
.kb-navigation > .wp-block-kadence-navigation-link > .kb-link-wrap > a:hover::before {
    width: 100%;
}

@keyframes growLine {
    from {
        width: 0px;
    }
    to {
        width: 70px;
    }
}