Disclaimer, I focus mainly on story driven games, so these ideas are rather story related than gameplay related.

Parasite - Either fantasy or scifi - you have a parasite/chip in your head and you two are arguing with each other. Your goal is to get it out (Cyberpunk, BG3 style)

Unusual communication - You have met some unknown entity, an alien, or some fantastical creature, and you need to figure out their language to understand each other. For example, a UFO crash landed. The ET needs help, so you need to translate what they need.

No text in the entire game - You are in an old ruin underground (something like Pyramids), and you have to figure out symbols and meanings of everything around you. There is no text anywhere. Not even the main character tells anything.

Side effects

Leave something behind - You write a book. But I have no idea how to pull this off haha.

Strange machines - I don't know anything now, but I freaking love drawing robots, so I'm sure I will be happy with this haha.

Voyage - You are traveling in the sees in the 19th century. You are attacked by a mysterious creature (Mobydick, Kraken...).