A quick search lead me to these sites, which I guess will do the job, but I haven't verified if they're working or not. It seems at least some of them will add some public trackers to the magnet link, but, with DHT enabled in the client, I think it could also work without adding those.

• https://www.hashtomagnet.com/
• https://magnetlinkgenerator.com/
• https://hardrisk.github.io/magnet/

or

• https://hash2torrent.com/%7Binfo-hash%7D (replace {info-hash} with the actual hash without the curly brackets to get the torrent file if peers are available)