Gallium nitride is a replacement for silicon in transistors, and you haven't heard anything because they've won. Any USB-C PD charger you see that provides more than 50W or so and isn't a gigantic brick is a GaN charger. Take a look at any reputable manufacturer's site and you'll find a section about how their chargers use gallium nitride transistors, e.g. https://www.belkin.com/products/product-resources/gan-charge..., https://www.anker.com/ganprime, etc.
The funny thing about big innovations like GaN is that they become mundane and invisible after the hype, but end up in a lot of places without most people realising it (like for Apple users, it's not GaN chargers, it's just the MacBook charger).
Even graphene has a lot of real-world applications that are far removed from the sci-fi marketing of speculators, but offer a great advance over past technology.
Even graphene has a lot of real-world applications that are far removed from the sci-fi marketing of speculators, but offer a great advance over past technology.