If you have questions on how to accomplish something for your game, or aren’t sure if it can be done in the engine, feel free to create a thread asking about how to accomplish it/if it is possible in the “How do I?” section of the forums.
Community extensions are made by anyone and everyone that wants to make an extension. Generally you will want to find out if what you want can already be done in the engine first.
If you have an idea for an extension, you can always mention it in the “extensions-and-examples” channel on the discord server, or make a request to the team of community members that review new extensions on their trello, at this link.