Depending on your menu content, you might notice a slight shift of the content when you open a menu. This is a result of the scrollbar displaying and then hiding as the mega menu grows to the size of the content. To prevent this, add this bit of Custom CSS area
/*Prevent Layout shift with Megu Menu size change*/
.wm-mega-menu .mega-menu-item {
transition: opacity 0.3s ease;
}