You can fix this only in the file styles, it is better to create a child theme and there to make changes. To change the sticky menu, you need to open the file /wp-content/themes/fasto/style. css in line 1167 find the value-position: sticky; and change its value-sticky to “static” or “unset”. So far, this is the only way to cancel the sticky menu.
/* 6.Header */
header#theme-header{
display:flex;
padding:22px 70px;
width:100%;
margin:0 auto;
z-index: 10;
position: relative;
border-radius:5px 5px 0 0;
justify-content:space-between;
position: unset;
top:0;
box-shadow: -1px 0px 16px 0px rgba(0, 0, 0, 0.07);
}