Embedded systems is a very large area, so an overview might be a good way to get started. Shameless plug for a great book on this - Peter Marwedel's (my former boss at TU Dortmund) "Embedded System Design: Embedded Systems Foundations of Cyber-Physical Systems, and the Internet of Things"

The book is available as Open Access PDF at https://link.springer.com/book/10.1007/978-3-030-60910-8