[yxre]

I am also learning about the linux kernel, but not in an embedded context. Here are some good resources I have found.

https://man7.org/tlpi/ This book is considered the best overview of linux kernel interface. Its old, but still gives a broad coverage of topics.

https://lkml.org/ Browsing LKML is really helpful since it shows you where current development is happening and how kernel devs think. Some conversations get very advanced and nuanced.

https://kernelnewbies.org/ is a good starting place for starting to compile and deploying kernel builds

Other than that, reading and tracing the source is probably the most productive thing to do for an experienced dev to do