reddit.com is a popular one.
I always felt like vommiting when I saw people recommend /r/woodworking, but I couldn't figure out why. I was reading an unrelated critique of /r/fitness one day and somebody summed up my feelings about /r/woodworking perfectly
"/r/_______ is a bunch of beginners masquerading as experts."
Q: Does this keyboard support Linux?
A: The keyboard is advanced but you can not run Linux on the keyboard.
This is probably not what most people think of when they are looking for serious and in-depth Linux discussions.
The smaller subs have an entirely different culture and community. Any interest you have has a related sub-Reddit. you can search for them by clicking the 'more' link in the top bar that lists the subreddits.
https://www.reddit.com/subreddits/
Subcribe to the ones you like, and unsubscribe from all the defaults.
Also, r/DepthHub collects insightful and researched comments from all across Reddit.