The book I read on K8S written by a core maintainer made is very clear.
(I didn't have access to my email or Amazon account let alone my office when I posted so couldn't check the name of the book).
(edit: found the 3rd edition)
The CNCF ecosystem looked a lot different back then.
Then you can hit other resources (in my case working with a team who've been using K8S for a few years).
If you (or anyone else) has suggestions for something newer and covering more than just the core (like various different components you can use, Helm, Argo, ISTIO etc etc) then I'd appreciate it :-)