For me, it's any community of Tradespeople. I can find relevant manufacturer and adjacent code regulations for modern equipment or building techniques anywhere online. The problem comes from obscure-ancient technology that was discontinued 60+ years ago, the only references to those are on Reddit and very specific forums.

I recently ran into an electrical panel that was built in the 60's and was promptly made illegal (split bus residential panel, no singular main disconnect switch). Even being trained and educated as an Electrical Engineer, it only gave me the ability to understand what the panel was doing, not the history and use cases of the past (since their use in residential applications is obsolete). I was able to find discussions between inspectors and electricians, how things played out with local authorities, and the on going debate of their practicality by actual professors discussing regulations and safety. I will miss these resources if they become unavailable at a future date (the whole enshitification process).

That being said, places with higher than average traffic (like reddit now) tend to give a lot of crappy answers. Lot's of diy'ers thinking their way is best (whether it's code compliant or not), and others who don't care about discussion and only want to say you're doing it wrong because it's not how they would do it (and nets them the highest profit margin on a job). There's lots of owners out there that are probably afraid to ask a question now adays because of the responses (same linux community effect), even though the information around it could be important.