You can use http(s) links to download .torrent files. You can then open those .torrent files in the program you want.
Now, as for magnet links, Opera doesn't support them. It just passes them on to the program on your system that's set to handle them.
Open up a command prompt and run:
start "Magnet Test" "magnet://test"Whatever program opens up from that command is the program that Opera should open up when navigating to a magnet link. If no program opens up, you need to associate the magnet protocol with the program you want in the Windows Default Apps settings. If the program you want to handle magnet links isn't available for association with the magnet protocol, you can look in the program's settings to see if it has an option to do so. Some programs only have the option in their installer. In those cases, you might have to run the program's installer again.