I browse my LinkedIn feed (yeah, I know) and I often see discussions pop up between people from my network, albeit nowadays it's mostly about AI tools.

I see discussions pop up on /r/webdev on reddit, but not a super active subreddit.

on 4chan there used to be /wdg/ (maybe there still is, but i haven't been to that website in years at this point)

I bet a lot of discussions happen on Slack servers for specific frameworks, but I don't have a lot of experience with using those except asking questions in the #questions channels