Chrome doesn't open automatically magnet links anymore

There are two protocol_handler keys in the Preferences json object.

{
  ...
  "profile": {
    "avatar_bubble_tutorial_shown": 2,
    "avatar_index": 26,
    "blacklisted_credentials_normalized": true,
    "content_settings": {
      ...
      "ppapi_broker": {},
      "protocol_handler": {},
      "sensors": {},
      ...
    },
  "protocol_handler": {
    "excluded_schemes": {
      "magnet": false
    }
  },
  ...
}

Make sure to modifiy the one at the root. If you modify the one in the profile, it will be renamed to protocol_handler,* and considered invalid.

The accepted answer didn't work for me. I found a better solution, at least for Windows.

Create a .reg file (I opened a blank file in Notepad, put in the following, and saved it as 'Fix Chrome Magnet Links.reg', then ran it and restarted Chrome). Contents should be:

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome\URLWhitelist]
"1"="magnet:*"

Tested and working. With a bit of luck it will keep working across multiple Chrome updates, and is much easier to install.

This solution is adapted from https://t-e.cc/google-chrome-no-longer-displays-always-open-these-types-of-links-in-the-associated-app-checkbox-fix/

From a reddit post:

Some time ago Chrome removed the checkbox to "always open" a magnet or torrent link with an external app like qBittorrent.

This was done for security reasons and it may return at some point in the future, once developers have found a way to make it more clear to users what the risks are of allowing certain links to parse whatever data the creator of the link wants to an app (that may be poorly coded) and also once there's some sort of user interface to manage these permissions (up till now you can only undo those permissions by going to "Clear Browsing Data > Cookies and other site data", which makes no sense).

Anyway long story short, you can re-enable the option to have whatever link always be handled by its corresponding app, which saves you a lot of clicking on that stupid confirmation box for every magnet or torrent link you want to download.

Depending on the browser you use (Edge, Chrome or Chromium), add the proper line to your Windows registry. You can do this by saving the code below as a .reg file, for example ShowExternalProtocolWarningBypassCheckbox.reg. Or you can do it manually using regedit.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Edge]
"ExternalProtocolDialogShowAlwaysOpenCheckbox"=dword:00000001

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome]
"ExternalProtocolDialogShowAlwaysOpenCheckbox"=dword:00000001

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Chromium]
"ExternalProtocolDialogShowAlwaysOpenCheckbox"=dword:00000001

This has been tested on Google Chrome 79 running on Windows 10 Version 1909. There is no need to reboot, just close all instances of Chrome, run the .reg file or make the edits with regedit, then fire up Chrome again.

Now click a magnet link, check the box to always open them in qBittorrent and enjoy single-click downloads once again!

Source where I found all this info: https://textslashplain.com/2019/08/29/web-to-app-communication-app-protocols/

Original Reddit post: https://www.reddit.com/r/qBittorrent/comments/ewxq5o