thank you. for the desperate: this codes hides 1, 2 and 3 and displays 4, 5 and 6 (i have 6 header navigation links):
<style>
.header-nav-item--collection {
display: none !important; /* Hide all navigation items by default */
}
.header-nav-item--collection:nth-child(4),
.header-nav-item--collection:nth-child(5),
.header-nav-item--collection:nth-child(6) {
display: inline-block !important; /* Display the specific items you want to show */
}
</style>