If you are trying to understand the difference between the different cryptography-related formats (PKS#12, PKCS#8, PEM, X.509 certificate, DER, JWK, BEGIN ENCRYPTED PRIVATE KEY??? 🤯), you will hopefully find some useful information here (and a lot more your did not wanted to know about).
This post is an overview of the different tunneling options available in OpenSSH. This is intended as a reference to use when I am explaining (every so often) how to use SSH for tunneling.
While looking at the OpenSSH ssh_config manpage, I found the ProxyUseFdpass configuration I did not know about. It is apparently not widely known or used.