Sunk cost fallacy is probably the most obvious one that springs to mind. Not unlike gambling in a sense, people feel they just need one big payout to win it all back and then some, so they keep betting, hoping that this time things will go in their favour.
It used to in the past. It was removed in the 0.19.0 release. This is the pull request that took it out (I think).
This thread has some of the reasoning for it, but at a high level the Lemmy devs made a call that the benefits a karma system provide didn’t outweigh the problems a karma system can cause.
Have a look through the tools section on the Megathread in the pinned post. For this specific use case you’re probably going to be wanting to look at tools like Sonarr (for TV shows), Radarr (for movies), some form of torrent client that those tools support (Transmission for example), and depending on what your tracker supports, possibly something like Jackett to provide a bridge between your tracker and your downloader tool.
The benefit of this kind of setup is it’s very easy to add Usenet into the mix if you choose to.
There’s some extra steps needed if you run it directly on the Mac but you can also do something like run Docker on the Mac and run those tools within Docker instead.
I’m pretty sure it’s possible to integrate something like Overseerr (which is a web frontend for handing requests for new content) into the Plex watch list meaning you could add a show to your watch list in Plex, Overseerr would pick that up, send it to Sonarr or Radarr depending on the type of content it is, which would then do a search on your tracker for the content, send the torrent to your torrent client, and then when it finishes downloading automatically import it into Plex.