I wouldn’t expect all future animated adaptations to be PG-13 movies.
The PG-13 rating will allow the production to push things a little harder than they otherwise would.
It’s still technically available for wide audiences, nobody is restricted from seeing Cruella based on age.
But for those fans who might be looking for a somewhat more grown-up version of the Cruella de Vil origin story than a PG rating would provide, this rating is probably good news.