What to do if you can’t open a magnet: file in Chrome

This question had the same issue except with qbittorrent caused by trying to associate magnet links with a remote client in Chrome. Chrome has set itself as the only program capable of opening magnet links. You can see this by opening Windows 10 Settings > Apps > Default Apps > "Choose default apps by protocol". There is an entry for magnet links, that only has Chrome as an option.

Instead of associating with magnet links via HKEY_CLASSES_ROOT/magnet entry Chrome uses the newer URLAssociations. I don't know about µtorrent, but qbittorrent does not have a URLAssociations entry. Windows seems to prioritize applications with a valid URLAssociations entry over the HKEY_CLASSES_ROOT entry for said protocol.

tl;dr:

To fix it, open regedit, navigate to Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Clients\StartMenuInternet\Google Chrome\Capabilities\URLAssociations and delete the "magnet" entry.

https://superuser.com/questions/1535819/cant-open-magnet-url-with-google-chrome-anymore