What is the problem you’re seeing? All of the Markdown links in your GitHub example work for me.
Fragment links to headings probably won’t work in all Markdown editors. Some probably don’t support them. The ones that do, convert headings to URLs in different ways. You could use HTML to manually add IDs to link to, but probably not all editors will support them (if I remember right, Obsidian doesn’t).
But some editors provide a heading navigation feature like Obsidian’s Outline.