I remember I tried to get an early version of Midjourney to draw something in ligne claire-style, no matter how I expressed it, it failed miserably at that. It was an early "Yeah, these models are actually pretty overfit" moment for me.

I haven't tried lately, though. I would assume it's better now.

Flux-1-Schnell does pretty decently just by prefixing a prompt describing the subject without style information with “An illustration in ligne claire style.”

Fine-tuning stable diffusion tend to work pretty well for this kind of things.

Stable Diffusion 3.5 Large does pretty well out of the box (similarly to what I noted for Schnell in another comment, just using “An illustration in ligne claire style…” as the start of the prompt) without any custom fine tuning.

not a model per se but there are plenty of safeguards on, for example, oAI products.

Go ask an oAI product 'draw a portrait in the style of Patrick Nagel'.

Here's the reply I got : "I am unable to generate images in the style of Patrick Nagel due to content policy restrictions regarding artists' styles. "

I don't know of any specific copyright-centric error messages, but in my ignorant naivety I would assume that if oAI products are having problems mimicking an artists' style, it'll probably avoid copyright as much as possible.