May have missed it? I don’t see any links that specifically filed copyright on “Gameplay only” can you point out? I remember back in the days Nintendo had issues with a game that looked and played too similar to Mario and they created problems for the other studio but that was long ago when Mario was a novel thing and now there are a thousand mario ripoffs. Then again Ningtendo are well known for being extremely picky with their titles and go after everybody for anything.
Personally I have never come across a game that specifically filed copyright on its gameplay. Gameplay falls within the concept of an “Idea” and you can’t copyright “Ideas” or a “Mechanic”.
Don’t go too far they tried to do this recently with “Battle royale” I think it was the case between Epic and PubG. It failed doesn’t work. now there are a million Battle royale spin offs out there.
But when it comes to Art, exclusive characters, Titles, music and code, then yes thats a different story.