How do I learn embedded Linux developpement

I already have a CS training and a good knowledge of C/C++. I played a bit with arduino electronics and raspberry pi (always with raspbian). I'd like to learn things such as buildroot and the device tree.

My first goal would be to hook a DPI LCD to a linux board (Lichee Pi nano) using an image I'd generate through buildroot.

Are there comprehensive ressources (free or not) for learning such things, like a book or an online course ? I feel like a lot of the documentation is hardly accessible for plain beginners and it would be perfect to have a more guided experience.

This series : https://www.thirtythreeforty.net/posts/2019/08/mastering-embedded-linux-part-1-concepts/ was very informative as an introduction but it'b be nice if I could go more in depth.

Many thanks