Yeah, 2019 was the year of the clawfoot bathtub (thread here). I nominated 2020 as the year of the peristyle (thread here), though there were other themes as well.
I’d second the extremely-online nature of 2021 – maybe a reflection of how many of us spent 2020? @aschultz, your spoilery example is good too , and I think there’s even a third example: the swamp in Libonotus Cup I think works via the same rule, though I haven’t played Finding Light so not sure if there’s a different mechanic you’re referring to.
EDIT: oh, there are also two sailing races when I don’t remember any other games with one: The Libonotus Cup, and my game Sting.