Spry Fox v. LolApps (2012) was a case about a similar visual and thematic remake of a game (Triple Town vs Yeti Town). The Yeti Town developer decided to settle when it became clear that they would likely lose, and the remake is no longer available.
Realistically, of course, it probably doesn't matter since I assume the author doesn't have the resources to fight Firaxis in court over this anyway.
> I assume the author doesn't have the resources to fight Firaxis in court over this anyway.
Bigger corporations than Firaxis have made that same assumption and lost. There was a great story recently about an Adelaide woman who represented herself in a suit against Google for years and finally won: https://www.abc.net.au/news/2023-10-23/janice-duffy-wins-12-...
The Spry Fox fact pattern is distinguishable, I think, given that the defendant had access to privileged IP and had been negotiating to port the app before creating the knockoff after negotiations fell apart.
Realistically, of course, it probably doesn't matter since I assume the author doesn't have the resources to fight Firaxis in court over this anyway.