There have been some decisions in that direction (https://www.nutter.com/ip-law-bulletin/no-dice-for-gaming-patent-under-35-USC-101 https://www.nutter.com/ip-la

There have been some decisions in that direction (https://www.nutter.com/ip-law-bulletin/no-dice-for-gaming-patent-under-35-USC-101 https://www.nutter.com/ip-law-bulletin/no-dice-for-gaming-pa...) but there's no per se rule against patenting game mechanics. Also, the story here is talking about Japanese patents. I have no idea if game mechanics are patentable there.