If you have an Intel CPU, there is a good chance you have a KVM built-in (whether you wanted one or not): Intel AMT. Its reputation was tarnished by Intel's dissimulation and opacity about the technology, and a streak of critical vulnerabilities disclosed in late 2017. I chose to take my chances with it anyway for my homelab server. It is secured with a password, mutual TLS (client has to provide a cert), and restricted to the LAN via a physical firewall. It gives me serial console, KVM, and power control.

I like it. It works pretty well. I don't see a reason to trust it any less than closed-hardware, closed-source solutions. I would trust a fully-open-source PIKVM more, however.

The tooling and documentation for setting up Intel AMT via open-source tools is meagre, so I had to roll my own. I only need a small nudge to package it for others to re-use, so reply to this post if you are interested.