Basic tool to export Unity Meshes to FBX, with C++ plugin I wrote using Autodesk FBX SDK
Add Editor and Plugins folder to your project, then you can call MeshFBXExporter.ExportMesh(...) from anywhere. Feel free to do whatever you want with it.
I included the cpp code if you want to change the plugin too but don't include it in your Unity project! you will need to compile it with FBX SDK include/libs on your computer. I might make a cleaner repo with all that later but can't be bothered for now, sorry!