Given that reddit surprisingly still has a working API, this isn't actually a hard thing to check. Here's a script that works courtesy of ChatGPT:
https://gist.github.com/bspammer/6b5eff6670e4b839ffea89ceaed...
The highest non-bot user moderates 12 subreddits in the top 100. There's quite a few users who moderate more than 5. I believe the situation was much worse a few years ago, and reddit the company put pressure on them to give up some of their subs.