In isolation, no. But the produced works can be too close for fair use (as demonstrated with the Prince pieces by Andy Warhol), and passing it off as a piece from the original artist can open you up to forgery/fraud charges.
To put another way, the motivations to produce art in another artist's style can still land the artist/buyer in legal trouble regardless of fair use.
Yes that is true, but I don't think the people who use style transfer are actually passing it off as the original, they just like it for the aesthetic value of their own images. In other words, no one using the Van Gogh LoRA is actually trying to forge the Starry Night.
Given the value of an "authentic" painting of the Starry Night (or more realistically the value of something forged in, say, Samwise Didier's style) I can't agree with "no one".
I have to imagine that it's likely quite popular to sell AI generated art that mimics or copies existing works.
Do you use AI art generators? Flaws are extremely easily found out, it is only good for a rough snapshot (without much fiddling and even then, artifacts remain). I can guarantee you it is definitely not popular to sell existing works made with AI, you are better off hiring an actual forger. In fact, your suggestion is even the first I've even heard of such an idea.
To put another way, the motivations to produce art in another artist's style can still land the artist/buyer in legal trouble regardless of fair use.