I mention in a footnote that the input has no non-alphanumeric characters is an implied constraint for palindrome problems. Just doing a two-pointer approach would fail the test case of "A man, a plan, a canal, Panama!" (an extremely famous palindrome) that iteration of the ChatGPT-generated solution also gives.
Another implicit constraint now that I'm looking at it again is that the characters are uncased, so the ChatGPT-solution would fail the test case due to the capital P of Panama.