Currently BiglyBt supports I2P and it has been that way for quite some time.
If you use qBittorrent, I2P support will come in version 4.6. you can try it out now with the published release candidate version. Probably other clients are working on it too as the support is coming from the libtorrent programming library, which is used by other clients too.
Right now, I2P is quite slow in my experience, in terms of loading I2P websites. I hope that it’s just a misconfiguration on my part, or that these specific sites I tried are just overloaded.