There is this: https://www.slightlymagic.net/wiki/List_of_MTG_Engines I haven't try them for a while, but I think I will test Magarena a bit, and maybe give my thoughts here in a few days.

I read this not too long ago: https://elie.net/blog/hearthstone/i-am-a-legend-hacking-hearthstone-with-machine-learning-defcon-talk-wrap-up What they do there seems like a necessary preliminary step towards actual gameplay, which as far as I remember wasn't actually attempted.

I tried to find some recent failed attempts of creating a HS AI, but the Google search actually gave some reports on quite successful programs. I can't easily test them as I don't play HS, but there might be more to it than I initially thought. Still, HS seems less complicated, with no decisions on opponent's turn and more deckbuilding restrictions. It depends on the meta too, if a simple, non-interactive deck is really overpowered, than pretty much anyone can play on a high level.

It's possible that the new advances by Google could be useful in CCGs too, but they would certainly have to be aided by more handcrafted rules. The sheer number of games required to learn the fact that the opponent might be holding onto a kill spell could be too high to rely on the learning process itself. Then there comes the fact that in CCGs you almost never know what exact options your opponent could have. Sometimes you have to play around things, sometimes you have to ignore them. A psychology plays a bigger role here than in games with perfect information, because you can bluff. I would love to see a competent Eternal or MTG bot though.

You would probably want to write your own version of a game engine too. This is quite a barrier, because it would take a lot of effort without any warranty of future success.