Many of those I frequented are now privated, many have been banned for having no moderators, discussion quality has become abysmal (i'm very glad that HN has collectively managed to resist reddit-style "humor" comment chains so far), the frontpage/default subreddits are full of politics, bots, karma farmers, sob stories and ragebait.

But which subs? You didn't answer...

r/astrophotogramemes for one, but also many other smaller/niche ones I can't even remember nor find anymore since I stopped using them a while ago when this happened - I deleted my reddit account.

I often check out the LaTeX subreddit and I perceive the number of posts are down, even with a pretty recent new mod, who was doing a good job.