That is/was a Chrome problem, Firefox only allows WebMIDI after granting permission. Unfortunately its implementation is also incomplete/buggy so I still often end up using Chrome for those use cases anyway.

As I understand it, it was because WebMIDI was accepted by Chrome without prompting the user.

To me it seems should be impossible use it for tracking after they added the prompt.

Whenever the committe crams another desktop features into the browser you can be sure it is mainly convenience and surveillance!