Copyright in my understanding is the creator/owner’s right to prevent unwanted usage, imitation, recreation (in addition to many other things) of their work. They have the right to control how their intellectual property is being used by others. Creators/owners rarely pursue legal action against those creating fanfiction that involves their intellectual property unless that fanfiction gains traction that could lead to profit. Unfortunately, copyright seems (to me at least) to have become way less about protecting intellectual property and more about protecting and pursuing profit.
I’m not sure if this counts or if there was any kind of legal action that was taken here, but I think of the feature of Instagram’s “stories” as a possible violation of copyright law. Snapchat (as far as I know) came up with the concept of having users be able to post “stories” for their friends (24-hour posts that can be easily scrolled through). Instagram introduced a practically identical feature to their app. I’m not sure if this violates copyright law, as “stories” may not be considered intellectual property, but it’s possible.