I've tried LFS about 15 years ago. It actually teaches you better to learn the inner workings of Linux if you follow Gentoo (or the likes) that makes you actua

I've tried LFS about 15 years ago. It actually teaches you better to learn the inner workings of Linux if you follow Gentoo (or the likes) that makes you actually type in each of the steps to get the OS running like setting up swap and configuring kernel options but LFS tells you what the OS is made of like what packages are required to get a minimal system going. Good to learn both if you're interested.