When my blog and books are not enough, and you want to master a topic faster and deeper, you can take a course
There are a lot of courses out there, but here is my selection on Udemy
Beginner course
A-Z guide to understand the features of your Pi.
Learn basics and build your first hardware project
Check the course details
Retro Gaming Machine
Learn how to build you own retro gaming machine.
Lakka, Recalbox and Retropie are at the program
Check the course details
Python Masterclass
Python is the main programming language on Pi.
You'll learn in this course everything you need about it
Check the course details
Hacking with Pi
Learn ethical hacking with your Raspberry Pi.
Use it for penetration testing and security auditing
Check the course details

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I recommend these products because I use them myself and I know them.
This is simply a list of what I use and love