I also don’t know them in depth, but from what I do know:
Lineage is a tweaked AOSP, it doesn’t have google apps by default but can use MindTheGapps or microG
/e/OS is either their own system or heavily modded android, iirc it uses microG by default (mG is by /e/ i think)
Graphene is a privacy-focused android mod that can use googl.e apps, but in a sandbox. Basically a separate space, where they don’t have any access to outside data

So basically they all lack google by default, but with different ways to use apps that use google

Yeah it is. Just “deGoogled unGoogled” as they say

Degoogled android

There’s already a project like the first thing you wrote, SPIRIT, built on top of a rpi cm5, currently in ideas and mb design stage

KZ reminds me od Kaizen from Event[0]

Afaik, yes

Joe mama