"The Princeton Companion to Applied Mathematics" is an overview of Applied Mathematics, some applications of different areas of it, brief introduction into problems and areas. More for curiosity.

This book is a textbook. It is "Foundations", good proper introduction, it does not go very deep, but it builds solid background. It's is actually going to be 4 books, so tons of knowledge.

Moreover, here: https://foundations-of-applied-mathematics.github.io/ you can find labs and materials in Python to back reading with practicing.