Games You Can Play With Only Your Mind

So there's a singular book on this topic I've seen mentioned elsewhere

but it's an independent idea that's popped in to my head related to the other post about daydreaming (and I haven't read the book)

about "games" or playful things you can do in your head; it's interesting to me the ways in which your head cannot duplicate games, like how video games might keep score automatically (I think I would struggle to remember all kinds of scores and points)

Essentially the book referenced elsewhere sounds like they give you a topic and you kind of make up a story from it in your head; like a solo roleplaying game?

I find my "mindgames" are more of a "freestyle" without necessarily a narrative: [take the random science] name "blue dwarf" [which] might remind me of "green leprechauns" which then makes me think of "green dwarves" (which are nonexistent stars I think, no "green dwarf" stars exist?). This isn't necessarily the best example, but my "mind wandering" I often try to direct towards something practical, like maybe building something new that could be used for a practical purpose. Maybe even "green dwarves" could be a title used for some other project. Well, looking up "green dwarf" on a search engine gave me this article, whatever it means, but in any event these ideas kind of freely bounce off each other and sometimes combine in some useful or interesting way (at least to me); perhaps this process really needs no description and is obvious (but I'm not sure how many people make use of it): https://www.scientificamerican.com/blog/observations/in-search-of-green-dwarfs/

I saw some other games that people liked to play, like coming up with some noun for each letter of the alphabet a-z in order; this is something different than the story or freestyle ideas, but I guess you could spin off stories or free associations from the letters.

This is just a sampling of the kinds of games one might play in the mind...

has anyone thought of games they can play in the head, or have favorites or tips on this kind of "gaming platform"?