A human artist can freely paint something in the style of another artist. It's not considered a derivative work. You can't copyright a style.
A derivative work is an adaptation, translation, or modification of a particular, existing copyrighted work.
If you asked Stable Diffusion for "Vincent van Gogh's Starry Night with a cat looking at the sky", you'd get a derivative work (although Starry Night is in the public domain, so you wouldn't be violating its copyright).
A derivative work is an adaptation, translation, or modification of a particular, existing copyrighted work.
If you asked Stable Diffusion for "Vincent van Gogh's Starry Night with a cat looking at the sky", you'd get a derivative work (although Starry Night is in the public domain, so you wouldn't be violating its copyright).