Ever since the migration from the old forums.adobe.com to the new community.adobe.com forums, I've been working to find a new home for the previous Add-ons/Extensions forum: https://forums.adobe.com/community/creative_cloud/add-ons/extensions
Initially, threads migrated from Add-ons/Extensions were moved to Get Started -> Exchange: https://community.adobe.com/t5/get-started/bd-p/get-started?page=1&sort=relevance&filter=all&topics=exchange This was not ideal, since "Get Started" speaks to either Creative Cloud beginners and/or forum newbies. Many people who distribute on the Exchange are advanced Creative Cloud users, long-time scripters, developers, and coders.
Although absent immediated after the initial migration, many scripter/developer subforums have returned under their respective product umbrellas, for example, the Premiere Pro SDK area, although absent initially, has since been re-created by community members here: https://community.adobe.com/t5/premiere-pro/bd-p/premiere-pro?page=1&sort=relevance&filter=all&topics=sdk
In case you happen to be looking for one of the old sub-forums, I have come up with this chart:
Let me know if I've missed anything.
Stay tuned as many threads from before the migration are scheduled to be restored from the archive later this month.