Triple A people: Do you use automatic navmesh generator for pathfinding system?

I am trying to understand how to create a navmesh and I have seen people in game dev industry manually creating navmeshes for the maps. Is this the way or does everyone use some algorithm that automatically generates navmesh?

As for the auto generating of nav mesh, I cant find resources online on how to generate triangles inside of polygon that has other polygons inside of it which are the obstacles.

How do people do it?