That wouldn’t help much. Consider a toy example: maybe the AI uses the letter “v” much more often than humans do. You’d need to make enough typos to shift the frequency of that letter all the way from the AI distribution to the human distribution. If a human would typically use that letter 5 to 10 times and the AI uses it 25 to 30 times, one typo won’t make much difference.

Real AI watermarks can use more sophisticated patterns than letter frequencies, but the basic idea is similar: the watermark is spread across many choices in the text, so changing one character generally doesn’t remove it.