Honestly, meme communities' comments could have some of the best in-depth discussions. Memes tend to provide a great launching point for discussions. A sort of prompt that everyone can coalesce around to talk in a serious manner about the subject.
/r/dndmemes and /r/programmerhumor were two great examples.
There are serious programming subs. However, I find that those tend to debate/discuss solutions/approaches moreso than the actual code itself, although that's not unheard of either. For actual coding questions, I want to say there's a "learn programming" sub that has those, but they're pretty strict about just doing people's homework for them (those posts tend to be pretty obvious).
The validation system is extremely off-putting. I have been working on some specialized tools for years so I could have answered some very precise questions with good confidence. However, the system was always there to detrust me and I was not going to spend hours to go through their hoops for an answer that takes me 10 min to redact. So instead I'll post it on Reddit or a gist hopping people will be able to discover it.