Note: this is a work in progress. Many improvements are needed. For better normal maps generation, please use Laigter. Its also free and opens source.
This plugin creates a dock that lets you open a texture and create a normal map for it adjusting a few controls. The normal map is exported in the same directory than the original texture, with a "*_n.png" prefix.
If you know how to use godot, any help is welcome! (Help is needed specially in GUI). The plugin is free and open source, but you can also support this (and other of my projects) by buying the pluging here.