I would also like to ask about art, is texture in the form of noise or shadows on the edges of the object also prohibited or not? Not those created by the shader, but those drawn by hand.

Small discrepancies due to pixel resolution are not a problem. What matters is that the shape is still clearly recognizable as one of the allowed shapes (circle, regular pentagon, sphere, right square pyramid). Minor jagged edges, pixel steps, or slight rounding errors are fine.

However, be aware that pixel art and pixels often shows as squares, and squares are not one of the allowed shapes. Make sure your art still looks like the intended allowed shape, not like a square(s).

Textures, noise, shadows, highlights, and lighting (engine-based or hand-drawn) are allowed and can be used for style or atmosphere, but be careful with noise, as it can sometimes form or suggest other geometric shapes (like squares or hexagons), which are not allowed. The underlying silhouette must always stay clearly recognizable as one of the allowed shapes.