Dear Zonndek,
Please add the given CSS code in Aditional CSS
Appearance > Customize > Additional CSS
@media screen and (max-width:992px){
.online-shop-enable-sticky-menu .responsive-slick-menu {
max-height: 500px;
overflow-y: scroll;
}
}
Note: Change the value i.e. 500px as per your requirement. !
Best Regards!