ChatGPT is a terrible proof reader. I fed it some of my own text with obvious errors in expression and "wrong words" (they're, their, there) deliberately injected and it failed to pick up on them.

In my mind, the best proof read is "Reading it out loud". :)

The thing I find most useful for these tools is to expand my own thinking process. I try to get it to act as a "journalist" and "interview" me about my ideas, so that I can clarify and distill them further.

Sometimes the right question is just enough to get me truly focused on what I am trying to say or achieve - not only in fiction, but in creative non-fiction, too.