I haven't seen any recent (last 5 years or so) articles by him showing he's doing any work on it. There's a few recent articles where he talks about how humans should work with machine learning, but nothing specific.

When he recently came out of chess retirement he didn't talk about it at all in either 2017 or 2019:

https://www.telegraph.co.uk/news/2017/07/06/king-back-chess-...

https://www.theguardian.com/sport/2019/sep/06/chess-leonard-...

There's nothing recent about him on https://en.wikipedia.org/wiki/Advanced_chess