Well, there is a lot of research going on in every direction, although most of the breakthroughs are on the applied side. And as you can imagine, the current development of new applications, architectures, loss functions, optimizers etc etc is way to fast to have rigorous theory keep up with. So don’t worry if you read a ten year old book, because it should still give you a good idea of the foundations. After learning those, you can pick what is the most interesting to you and read papers to see how it is applied to modern models and problems.