Jira Plugin Development where to start

Hi I’ve Recently gone through the tutorial available at https://developer.atlassian.com/server/framework/atlassian-sdk/create-a-helloworld-plugin-project/

This was a good introduction but feels like it touches about 1% of capabilities.
There is some potentially good documentation at https://developer.atlassian.com/server/framework/atlassian-sdk/plugin-modules/ but tbh the learning curve seems rather steep.

Can anyone recommend any other resources I can use to get a better understanding of the capabilities.

Are they any good public projects available as reference?