I _had_ to learn k3s specifically when I got to my current job. The first month was literally a tiny bit of onboarding, and then the person that was then-currently managing the cluster and Linux infra...being unceremonosly (<- how do you type that actually? xD) fired - and me being told to take over their duties... in full.
So, k8s.io docs, cover to cover it was. XD Could say that the real apprenticeship I am having is as a Kubernetes admin, if anything, because thats the only new stuff I learn. o.o
With L4 in the cloud, you probably mean Layer 4...so, a load balancer? I just have a VPS for 8 bucks that reverse-proxies home through a Headscale VPN. How exactly did you configure your l4 to "phone home"? o.o Wireguard or something?