Hi! I found your tool on the Godot AssetLib and had tried to download from all sources (GitHub, Itch and Godot Asset Library). I have found that your demo works as expected but I have not been able to extend it to my own projects.
I'm not sure what's the exact cause of the problem, but I can't seem to expose the export_custom for the Inputs and Animations to the editor. Your demo with the character already set up has them on the editor, but if I try to make a new character using the same script, they don't have the inputs and animation exports. If I detach and reattach the script to the character in the demo, it wouldn't show up as well. If I change the PROPERTY_USAGE flag to something like PROPERTY_USAGE_DEFAULT, it would expose the Dictionary object, but not the list of button like yours has. Adding key/value to the Dictionary don't do anything either.
Other weird errors also pop up like the AppliedValues object is instantiated but not assigned to the variable in the Controller object. I'm still trying to figure out how I can use this tool in my own projects. Any help you can offer is appreciated.