This is a paid asset, but now you can download RuntimeFbx Lite for FREE, but please remember this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Detail this asset from Unity Store: Original Link
RuntimeFbx Lite v0.0.1
A FBX toolkit that create/load FBX from/into Mesh at runtime or in editor.
Provide programming support to
create fbx file from a Mesh at runtime
load fbx file into a Mesh at runtime
Content includes
Class library that provide programming API
runtime demo
editor demo
Works in various environment
Support both runtime and editor
Support all system that is compatible with .NETStandard 2.1+
Support Unity 2021.2+
*Material, Animation and Skinmesh(BlendShape) support are under development and will be available in RuntimeFBX Pro.*
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Third-Party
RuntimeFbx uses
1. SharpZipLib under MIT license
2. DragDropHandler.cs under Public Domain
3. icons from flaticon and freepic under Free License with attribution
See Third-Party Notices.txt file in package for details.
Features
create fbx file from a Mesh at runtime
load fbx file into a Mesh at runtime
Supported OS
All systems and platforms that are compatible with .NETStandard 2.1+