SimilarWeb reckons ChatGPT usage is dropping (according to this Reuters article).
See also this report from back in July 2023 reporting on a 10% drop in web traffic to the ChatGPT site.
Note: this is only looking at web traffic trends, ie it excludes apps and API traffic (which one would assume is growing).
Difficult to say what this means for ChatGPT (versus AI interest in general), but given how many competitors both large and small have popped up in the last 6 months I doubt anyone is surprised.
Kind of amazing that the web traffic alone is still so high in my opinion.