There are a number of books written to discuss software development on Cortex-M. Examples include:
Arm offers a free of charge Arm Helium Technology M-Profile Vector Extension (MVE) for Arm Cortex-M Processors e-book.
Arm offers introductory Arm Architecture on-demand training courses, including M-Profile architecture, and appropriate development tools.
Coursera offers Arm Cortex-M Architecture and Software Development Specialization , a collection of online training courses.
Arm Education provides a number of resources to support STEM education at school and university level.
Arm also has a number of Approved Training Partners who can provide training courses to meet your needs.