No, game mechanics aren’t subject to copyright law. Game mechanics can be patented in the US, so long as they’re unique and nonobvious (to someone with ordinary skill in the field).
Monopoly and Magic: The Gathering both had patents on their mechanics, for example.
And of course, patents in Japan are a completely different animal than patents in the US.
The article you posted is from 2023 and PERA was basically dropped. However, this article talks about PREVAIL, which would prevent patents from being challenged except by the people who were sued by the patent-holder, and it’s still relevant.