This page https://support.kraken.com/hc/en-us/articles/9829766858260-Connecting-to-Kraken-s-Lightning-node on the Kraken support help center says which public key etc to use to connect to Kraken's Lightning node, and the conditions for doing so (0.01 BTC min)

I downloaded and installed a LN wallet called "Zap" which was on the list of recommended LN wallets at https://www.nicehash.com/blog/post/recommended-lightning-network-wallets and it is open-source, self custodial and runs on macOS.

But when I went to open a channel in Zap, and I pasted in the pub key of Kraken's Lightning node, it first said "No results", which I thought was confusing.

However, after keeping the program running and keeping this window open, it eventually found the Kraken Lightning node that I had searched for.

Hopefully this is helpful to others as well.