Currently not possible. Bitmagnet would need to have new code to be able to properly talk to the mainline java I2P service to enable DHT over I2P bittorrent. Or the Bitmagnet devs could develop their own I2P service to talk to the I2P network but that might be even more dev work.
https://github.com/bitmagnet-io/bitmagnet/issues/303
Per https://geti2p.net/en/docs/applications/bittorrent
DHT support requires SAM v3.3 PRIMARY and SUBSESSIONS for TCP and UDP over the same session. This will require substantial development effort on the client side, unless the client is written in Java. i2pd does not currently support SAM v3.3. libtorrent does not currently support SAM v3.3.
Correct. To be fair both XD and qBittorrent don’t support DHT over I2P so they’re kind of on the same level there. I think (?) neither support PEX over I2P either though I’m not 100% sure on XD about that.
https://github.com/qbittorrent/qBittorrent/issues/19913
https://github.com/arvidn/libtorrent/issues/7408
https://github.com/arvidn/libtorrent/issues/7269