Welcome to the community and congrats on your first plugin! Unfortunately, there really isn’t much documentation on this, and no tutorials that I’m aware of for debugging. That being said, I’ve just spent some time learning this myself, so maybe I can help out.
This is how I got to the sources for my plugin to do step-by-step debugging:
If you’re not seeing your plugin here, you may not actually be loading it correctly. Can you share your index.js file so we can see how it’s being loaded?
Sorry, I should have been more specific. There’s also an index.js file in the src directory that should look something like:
import { registerBpmnJSPlugin, registerBpmnJSModdleExtension, registerClientExtension } from 'camunda-modeler-plugin-helpers';
import ModelPlugin from './ModelPlugin';
import props from './bpmn-js-extension/props.json';
registerBpmnJSModdleExtension(props); // if you're extending the moddle with specific extensions
registerBpmnJSPlugin(ModelPlugin); // if you're adding to the Modeler itself.