This reddit comment shows that there is one association that was missed. In Computer\HKEY_CURRENT_USER\SOFTWARE\Clients\StartMenuInternet\ you should be able to find the name of the Chromium browser and then you have to go to Capabilities\URLAssociations and delete magnet from there.
Feel free to close this as I believe it will be linked to the old one anyway: https://github.com/webtorrent/instant.io/issues/244
Another solution for people who are stuck in this hell: https://www.reddit.com/r/torrents/comments/fjx3ef/comment/fkpon97/
This reddit comment shows that there is one association that was missed. In
Computer\HKEY_CURRENT_USER\SOFTWARE\Clients\StartMenuInternet\you should be able to find the name of the Chromium browser and then you have to go toCapabilities\URLAssociationsand deletemagnetfrom there.That finally fixed it for me.