I cannot recommend more to try the Ray Tracer challenge and if possible without AI.

It helps you build a full ray tracer / 3D engine only guided with tests, really powerful to learn test driven development.

What s cool is that just being driven with tests still allows you to do it in any language you want.

Plus you ll learn a quintillion of stuff about mathematics. This is really the kind of project that makes you go to a real senior SWE