If you convert a magnet link to a .torrent file (there are many sites that can do that) and then upload the .torrent file to archive.org, they'll download the files to their servers as part of their archival process, then you can just download the files via standard https, you ISP will only know you downloaded from archive.org.
But archive.org isn't really meant to be used this way, so this is probably unethical. But I think section 230 protect them (for now), so its not like they'll get shutdown or anything (correct me if I'm wrong).