Traditionally, extension sub-forums have existed and been pretty much dead-zones on the GMC, with very few people participating in conversations or even creating extensions. That doesn't mean I'm not open to trying this again, but I would say that we
currently have a forum which is underused and which is 100% appropriate for posting questions about extensions, or other languages being used in an extension, or even showing off stuff and getting feedback, etc... Note that it's a
discussion forum, not a straight Q&A forum, so it's perfect for what is being asked for.
I would have agreed with you if YoYo and other Marketplace vendors didn't become so negligent in upkeep for their extension offerings.
It used to be the case that a few people would create extensions, and then lots of people download them without much need to engage in conversation. These extensions tend to be long-lived without frequent modifications, and generally well-designed, trouble-free and adequately supported while active. In particular, the GMAPI in legacy 8.0 provided a documented interface for interoperating with internal GM runner hooks (albeit an unofficial result from reverse engineering), so the extension landscape was in a good position to fluorish in that timeframe.
This is no longer the case with the faster release cycles of GMS 2 and the shifting mobile development landscape. Extensions can come apart instantly between runtime updates, and to date there is still no formal equivalent to GMAPI in the extension mechanism. Whereas the probability of self-servicing is negligible in legacy times, it is almost certain today. Extension vendors on the marketplace are either abandoning extensions on a whim, not doing timely updates, not offering enough variety to suit contractual obligations (e.g. using a specific but new/uncommon ad vendor), or overcharging in a virtual monopoly. YoYo isn't doing much better, with the last updates to official extensions being at least one year behind on virtually the entire roster and most the related tutorials gone with the GMS 1.4 sunset.
By providing a dedicated place to help people learn to make and service extensions, you empower current and prospective commercial GM users to control their own GM destiny. Developers can start simple integrations on their own now instead of having to "buy" basic functionalities, and API vendors now have resources for integrating with GM properly (and no, just returning reals and strings is NOT enough). That way GMS 2's commercial use cases won't rest entirely in the hands of a few vendors (many of whom I think have been completely irresponsible), and professionals won't be forced into abandoning GM because of the general incompetency in the extension development landscape. They will be part of its rebirth.
As for publishing the extensions that are made, we have the Marketplace forum for that and we won't be making any forum specifically for sharing extensions.
Like I say, I'm open to this suggestion, but currently I can't see any need for a separate forum section... convince me otherwise?
We are not asking for a place to share extensions, we are asking for a place to learn how to make extensions and how to manually service them in emergencies.
Extension techniques are becoming a distinct use case in its own right, and the today's circumstances demand a grasp of it for all current and prospective commercial GMS 2 developers. The use cases range from simple (e.g. removing a single permission) to advanced (e.g. interacting with system-level hooks that may not have been adequately documented), so I would NOT agree with lumping it all into Advanced. And given their platform-specific nature and requirement of knowing other languages, I would DEFINITELY NOT agree with lumping these concerns with other advanced topics that are purely algorithmic and otherwise doable entirely within the GML domain.
The helpdesk articles are a good starting point, but they are entirely inadequate for the most common integrations needed in practical situations. Returning reals and strings and throwing a few Social Async events aren't enough. Details such as listening for system events (e.g. intents from API vendors, deep-linking, carrying out other actions in mobile exports, etc.) and data type interoperability (e.g. drawing on the application surface from an extension, handling/returning buffers from an extension, etc.) are now mostly unwritten knowledge, but are essential in doing things right. So having a place where we can publicly discuss and document these in a learning-oriented setting is essential and not fulfilled by any existing GMC or YoYo resource.