This is a somewhat different take, and quite possibly impractical.
The main thing I've done over the years to get reasonably 'good' at the Linux kernel (and quite a few other things) has been to read every technical article appearing in https://www.lwn.net/, every week, in full, even if I didn't really understand the material. I've been doing that since 1997, and it's paid off quite well.
Also: please buy a membership, even though you don't have to. It's well worth supporting.
The main thing I've done over the years to get reasonably 'good' at the Linux kernel (and quite a few other things) has been to read every technical article appearing in https://www.lwn.net/, every week, in full, even if I didn't really understand the material. I've been doing that since 1997, and it's paid off quite well.
Also: please buy a membership, even though you don't have to. It's well worth supporting.