I enjoyed the Microscope! But that one is very much on the creative writing side. Simmilarily I did enjoy Quiet Year.

Several of those map-making/settings building should work well. I wanted to try Gun & Slinger, but that one wants to be 2 players and a GM so I didn't try that one yet.

A couple of friends do a 1-player (and 1 GM) game in the Chronicles of Darkness setting (https://en.wikipedia.org/wiki/World_of_Darkness). It focuses a lot on mystery and investigation so it seems to scale pretty well to differing group sizes. While I don't play in that game, I assume there is still much of the usual prep work done on the GM side so it may not quite fit what you're looking for.

Gumshoe is a family of mystery RPGs and they've come out with a spin off system Gumshoe one-2-one for a single player and GM. There isn't a base book for the system but specific ones for Cthulhu, sci fi, teen detectives etc. Ironsworn and it's sci fi spin off Starforged also work well one on one.