Unfortunately, the URL of a page does not change when scrolling. The fibery forum (which is a Discourse platform) does have that functionality, but Fibery does not yet.
This is actually a bug in fibery (please create a bug report) because an anchor link should work in all cases to redirect to the header it belongs to.
How to reproduce: Click an anchor link, it works one time. Scroll away on the same page, the anchor link does not work any more, because the URL of the page is the same.
Use case: when you create a navigation menu with links to either anchors in the same page or in other pages, in any of these cases the anchor links only work once, until you click a link with a different URL.
Other bug: Loss of anchor when mentioning. Related to anchor links is that if you paste the anchor link somewhere and then click ‘Mention’ in the link menu, the anchor part of the URL is lost, and it becomes just a page link. So the mention feature has not integrated the anchor link feature. See also this post.