Figured out magnet links via the web ui, so posting if it might help others utilizing the forum search. They are tricky, even more so if you are using chrome (on Win 10, probably 11 too).
Magnet requires QBT running the web ui in HTTPS. To do this we need a self signed cert.
Pop open a console for this docker container, then make a new directory with `mkdir /config/qBittorrent/config/ssl` and enter it with `cd /config/qBittorrent/config/ssl`. Create a new self signed key with `openssl req -new -x509 -nodes -out server.crt -keyout server.key`. Enter whatever you want when it prompts; don't enter empty strings.
Next, fix the damn folder perms! `chown -R nobody:user /config/qBittorrent/config/ssl`. Otherwise the files/folder are owned by root:root and QBT will error later on. Enter the container, Option -> Web UI, then:
Check "Use HTTPS instead of HTTP"
For Certificate, enter: /config/qBittorrent/config/ssl/server.crt
For Key, enter: /config/qBittorrent/config/ssl/server.key
Restart the container, and use the HTTPS in the url. The browser might complain about an 'unsafe' website, click advanced and proceed anyway. If you see the UI, all is good.
Next we have to associate the magenet link. In the web ui, click Tools -> Register to handle magnet links. The browser should prompt something, accept it. If you're running firefox, that should be it - you can click a mag torrent link and it should work (there might be another browser prompt). I recommend you ctrl+click the mag link, so it opens it in another tab. If you're using chrome however... you will need to do the below.
https://github.com/qbittorrent/qBittorrent/issues/12605#issuecomment-1385058678
I'm assuming there is a similar work around on on mac/linux if you are using chrome. Annoying this doesn't work eaiser, and there is this much work involved. Hope this helps!