I am working on a private capacitor plugin for android and ios but the official guide finished by saying upload to npm to use your plugin, I do not want to upload it to a publicly available resource.
How do you register a local capacitor plugin for both ios/android
You dont need to publish on npm to install it. You could do "npm pack" on your plugin folder and later on your app folder "npm install ../my-package/my-package-0.0.1.tgz"
Also, I answered a similar questions about making plugins. Please look:
How to embed third party framework on ionic capacitor custom plugin?
How to embed an Android library (AAR file) into a capacitor plugin?