Asking again: Large terrain navmesh generation strategy

I got 0 answers on this,by my opinion,very important question so I am trying once again:

I have a pretty large terrain 3x3 km .I need to set nav system for AI.When I generate navmesh for the whole terrain I am getting the error: maxVertices <65536 && maxIndices <65536*3 - which probably means that the vertex and index buffers can not contain more than those numbers of the attributes.Besides,the generated navmesh is so heavy that the scene hardly responds.So how can I maybe generate nav mesh on some parts of the terrain?Or smth else?Does Unity have any solution for this?

For those curious : I must have that size of terrain as my program must work with real world units. Thanks.

A little research on the matter suggests (judging by other unanswered questions) this is hack and workaround territory :wink:

However:

So how can I maybe generate nav mesh
on some parts of the terrain?

This suggests you have currently made your nav mesh a like for like replica of the original mesh - which would be the wrong approach. You need to research simplification and there are options to experiment with as described in the docs and elsewhere.

See also unity game engine - If a terrain size is larger than the maximum limit (i.e. 1024 tiles) of Navmesh / gridgraph, how to apply grid graph/Navmesh? - Stack Overflow