I had many candidates submit absolutely terrible cover letters clearly made by ChatGPT. The number one sign - it talks about their experience exactly in the order I listed it on the job post; number two - I don't get to know anything about the person. I asked them to submit a cover letter they wrote themselves, and while not everyone's writing was as good as ChatGPT can write, I got to know the person, and hired few of these who definitely wouldn't make the cut if I went by the AI made letter.
If you can have AI generate your letter so well I can't tell, you get a pass. Nobody was able to do that yet, though (or at least didn't admit to it, even though I'm asking after they are hired and saying that at this point it would only help them if they did so).