This is super cool, like everyone else they hit the limit pretty quick with Gameboy graphics and move up to gba/butano. this is the wrong place to ask this but would it be possible to get a demo of drawing a rotating sphere.obj and wrapping it in a globe (earth) texture? and then drawing city marker sprites (la, nyc, London, Tokyo) on top of the map. I've been playing around with this in rust in macroquad but struggling with doing this in butano since you seem to have the only really excellent 3d example, but i couldn't find any spheres in the source code.
super cool game by the way, doing 2d rendering of objects on tiny hardware like this at full frame rate is rather impressive.