This question is interesting, but difficult to answer.
Technically, “inventing” a new type of dog does not mean that a new breed has been created. For example: I’m sure you’ve heard of the “Labradoodle”, a mix between Labrador Retriever and Poodle. Both those breeds have been around for a long time. The Labrador was standardized in the second half of the 19th century. The poodle is even older, on portraits for about 400 years, preceding the organizations that can recognize an official breed – the AKC in the US, and the FCI worldwide.
The Doodle, though, is not a breed at all. The AKC and FCI don’t accept it as a breed because there is way too much variation in temperament and appearance. By definition, members of a breed have to share many characteristics.
If you’re actually asking about the newest recognized breed: in America, it’s the
Biewer Terrier, recognized on January 4th of 2021.