How do I assign magnet links to use qbittorrent?

I had the same problem and managed to fix it by setting the defaults for both gvfs as well as xdg.

check defaults with:

xdg-mime query default x-scheme-handler/magnet
gvfs-mime --query x-scheme-handler/magnet

and set them with

xdg-mime default qbittorent.desktop x-scheme-handler/magnet
gvfs-mime --set x-scheme-handler/magnet qbittorrent.desktop

Assuming you have a qbittorrent.desktop file at /usr/share/applications/

Probably not the best way, but I achieved this simply by uninstalling Transmission - which caused the default to switch to qBittorrent automatically.

To remove Transmission:

sudo apt purge transmission\*

If you have installed q bittorrent for the first time when you click a magnetic link it will ask you to launch an application. So you need to select q bittorrent.

on the left hand side you would see filesystem. select that. /usr/bin/ ...search for q bittorrent in that list. then click OK. The download should start automatically.