The extraHrefMatchers mechanism in pretty-text.js.es6 doesn’t seem to permit query strings or schemes without a ://…
In the meantime, you can paste the links in a code block for people to copy, e.g.:
magnet:?xt=urn:btih:e2467cbf021192c241367b892230dc1e05c0580e&dn=ubuntu-19.10-desktop-amd64.iso&tr=https%3A%2F%2Ftorrent.ubuntu.com%2Fannounce&tr=https%3A%2F%2Fipv6.torrent.ubuntu.com%2Fannounce
Let’s perhaps revisit this after IE is dropped.