Hello,
I have seen that there is a fbx - three.js link but only in one way. Use a fbx to produce a three.js .
Is it possible to build a fbx exporter ? (it is a proposal)
Currently you could use the GLTFExporter and then convert to FBX (perhaps via SketchFab).
GLTFExporter is probably a good place to start, or OBJExporter is easier to import and convert in other tools but doesn't support lights, animation, PBR, etc.
Some options for converting glTF to other formats are the unofficial Blender importer or aspose. We're working on more tools for that.
Most helpful comment
Currently you could use the GLTFExporter and then convert to FBX (perhaps via SketchFab).