To add to this:
Do this, but instead of “add the ones you want” just add Jackett, then go to their github (you can actually get there through the “add the ones you want” menu in qbit, click
search -> search plugins -> "You can get new search engine plugins here: [URL]" -> [In the sidebar of that page] click "How to configure Jackett plugin" -> click "Jackett" to get to their repo and "this address" to get the stuff to copy for your jackett.py file for qbit and stick it in the right folder, which will depend on your OS.
Every time I reboot or Jackett updates, it doesn’t work anymore. I have to reinstall. Then it’ll work until the next update and/or reboot. Repeat. No idea what’s up with it. On Windows 10.