Logic Game
I got this "Gravity maze marble run logic game" set for the kiddo from Amazon.
It had apparently won a toy of the year award winner in 2017. It was lauded for helping kids develop critical skills like logical reasoning and planning skills.
This set comes with some sixty challenges with incremental difficulty. Beside these brain exercises, the game also provides fun gameplay for kids.
It is not easy. Here we have the kiddo's dad telling me that he is having a bit of difficulty comprehending the game.