Gentoo is useless for learning how things work. Back in the 00s when I still had time to hang out at events it was always quite ridiculous at what kind of basic stuff the gentoo crowd got stuck at - and with the tooling 15+ years more polished now I’d expect what is actually going on is way more hidden than back then.
If you do want to understand how things work just build a minimal system - either on spare hardware, or qemu/kvm. Don’t go with systemd, or other fat userland options - that just makes you compile a lot of dependencies not adding value for learning.
Use some lean init (or just write one yourself), and some lean shell.