This answer expands upon the answer given by @ScottWelker.
There are some quarks when working with Azure DevOps and numbered headers.
If you want to refer to a heading with a number like
## 2.1 Heading
Add a bunch of filler here to space out the page.
You would expect to write
[2.1 Heading](#2.1-heading)
However this will first try to link to a DevOps item using #2
and render it as
[2.1 Heading](.1-heading)
which is no good.
What you need to do is to add a path to your current document (as if you were linking to an anchor in a separate Markdown document) and instead write
[2.1 Heading](./<link-to-your-current-md>#2.1-heading)
which will actually create the correct link to the numbered heading anchor.
Be aware that this is only the case for DevOps Markdown - for normal Markdown you would usually write
[2.1 Heading](#21-heading)
as normal Markdown will strip .
s and replace spaces with -
dashes.