I think @Cedric may be the best person to answer this because it deals with his awesome nav mesh plugin!
We are using the recast nav mesh plugin to generate our nav meshes. We then pass the navmesh debug into the webxr teleport module as the teleportation target - all works nicely. The thing that seems strange to us, though, is that now all of a sudden our users are able to teleport on top of the roofs of our environments, heh. The surface of our roofs are not visible from the top, so we are wondering if there are any parameters related to backface culling or anything else that we might be able to do to prevent the nav mesh from creating navigable areas on the roofs of our environments.