Pixel art paint programs are an underrated way to learn a lot about a programming language and how to apply various algorithms in that language. For the motivated learner they’re perfect as a third project once you’ve completed something like a todo list and pong. Easy to make as complicated as your ambition and skill level determine.
And then you get into things like mouse input, creating a primitive GUI or even windowing system, printing, saving/loading different file formats... (at least back the early days if you were using something like DOS that didn't have any of that)
