Piracy: ꜱᴀɪʟ ᴛʜᴇ ʜɪɢʜ ꜱᴇᴀꜱ

can they be added to the search function in qbittorrent?

Nearly all can. All the one's you'd want anyways work with Jackett. They don't work via direct plugins but just run Jackett, follow its instructions and connect it to qBittorrent and you're good to go searching just the same as before. Some annoying ones occasionally require setting up another software like Flaresolver but for the most part the big easy to get into ones that open their doors annually work without that.

While there will likely be some openings throughout the year the fact is most trackers open in the period from Thanksgiving/late November through early January. TL opens then basically every year, a number of more exclusive trackers do open signups then, some for only 24 hours so get an RSS feed of that and remember to sign up IMMEDIATELY as soon as you see a post as the post on reddit may have been made 22 hours into a 24 hour open window, you just don't know. TL though at least tends to stay open for several days. So if you have no luck before then, wait until that time of the year and then check daily or even twice daily if you can, once before bed, once earlier when you get up or lunch or after work, whatever.

One way to find a private tracker is to monitor /r/OpenSignups. I would suggest using the RSS feed so you can get notified of new posts. Most trackers are only open for a short time. Don't bother with the new trackers that constantly pop up, they don't have enough users to maintain a good ratio easily. Be sure to get into TorrentLeech next time they open signups, that's a good general purpose tracker and it's very easy to maintain your ratio there.

Another way is to get into MyAnonaMouse, Orpheus, or Redacted through an interview and use the invites forum to get into other trackers.

There are unofficial qBittorrent search plugins for some private trackers. If you can't find a plugin for the tracker you want, you could always use Jackett.