The change log on GitHub shows support for i2p for Bitcoin Core. Not sure how to apply it to LN (ie CLN or LND).
Discussion
The way I've been playing with it on Lightning is to just set up a normal server tunnel and make it accessible on the ports that LN normally listens on. I've been playing with that on test net.
It's not default supported like the Tor network, so it's a bit tricky to test that it's actually working and I don't think anyone is actually using I2P on lightning. (Due to the lack of default support.)