There are AI detectors, but those are unreliable. They sometimes even flag works written before invention of the AI ...
AI isn't that difficult to spot in writing if you understand what it really does.
First, AI isn't really Artificial Intelligence, not even remotely. It doesn't know what it is doing. It is merely a sophisticated script which calculates the probability that the one letter is followed by another, and spouts the words, without being aware of the content or context. "The AI" always loses the track of its own writing because it doesn't know what the words mean, and only lays them, without even the trace of intelligence, and in time, it is apparent after the while. It usually does something the human poor writer wouldn't. The continuity errors are very common and often feel jarring because they could appear in the frequency the poor (but still human) writer wouldn't do. Grammar checkers (which are "the AI" practically) also don't understand concepts and continuity, but they perform considerably better as someone with human brain is doing it.
A Google Translators, however, would always feel like AI. If your first language isn't English (my isn't) and you feed this through the AI translator, you would always get something that gets it off track. The "Korean novel" argument is wrong, imho, it's just a mechanical translator doing stupid thing, even if the writer is human. Spellcheckers are sometimes guilty of the same thing.
Second, the AI is a prude, like Royal Road mod on the ritual bath water. They will never do something edgy, sexy, or whatever. They will never, never do this "Computer generate Trump and Chris Christie Yaoi fanfic" and always refuse, or misunderstand.
All AI content is heavily curated, and when I say heavily, I mean HEAVILY. People try to feed it weird stuff all the time, and corporations literally have hundreds of the minimum wage slaves to comb through it.
So as a rule of thumb: AI writing is always curated content with no context and no continuity.
AI visual art (i.e. pictures) are in fact considerably better in fooling you, and it is common that the artists are accused of using AI even if it was their hand drawing all along, but they too lack consistency and context. They are, however, sometimes considerably less curated as they often run on the separated, downloaded stuff.