[Nexus]

Попробуйте так:

$(() => {
    const scrollTo = (target, duration = 800) => {
        if (!target) {
            return;
        }
        
        const delta = $(window).width() < 768 ? 0 : $('.header-nav').outerHeight();
        
        $('html,body').animate({
            scrollTop: $([target, `a[name="${target.replace(/^#+/g, '')}"]`].join(', ')).first().offset().top - delta
        }, duration);
    };

    if (location.hash) {
        scrollTo(location.hash);
    }
    
    $(document).on('click', '.header-nav__dropdown li a', function(e) {
        const $this = $(this);
        const hash = (this.href || '').split('#').pop();
        
        if ($this.closest('.header-nav__list > ul > li').hasClass('isActive') || !hash) {
            return;
        }
        
        e.preventDefault();
        
        scrollTo('#' + hash);
        
        $this.closest('.header-nav__dropdown').hide({
            duration: 100,
            complete: function () {
                this.removeAttribute('style');
            }
        });
    });
});