I've got a Pop_OS system76 machine that runs well straight out of the box. I love it and it's my daily driver. However I'd like to learn more about how it works, Linux internals and how to use it to the best of its capabilities. I want to learn about things like system-d Wayland, error logging (there seems to be a few of them) directory structure and drivers. For instance, how do I know that my and GPU is being leveraged to the fullest?
I DONT want to build a system from the ground up, which I expect to be a common suggestion.
I'd prefer to read literature, blogs, and articles relevant to me, my system and not dated.
One alternative option would be to get a Raspberry Pi (or similar SBC) and run it using command line only. You will quickly learn the basics of Linux internals (directory structure, systemd, common command line tools and approaches).
Raspi isn't necessarily the best option for that, because it's based on an ARM processor rather than the x86_64 that's common on desktops and servers.
A cheap N100 "NUC" style Micro-PC is almost as inexpensive as a raspi and wouldn't limit the user to ARM-compatible software or add complications like emulating the architecture via qemu.