Fixed obstacles on a navmesh

How to bake fixed obstacles on a navmesh?

I found this in the Unity Reference Manual:
Fixed obstacles on a navmesh can be set up as part of the baking process.
but I can’t find anywhere that it explains the process…

I understand how to dynamic obstacles to game objects, but would like to add static obstacles in the bake…

Have you marked the obstacle as static (at least Navigation Static)?