You also don’t know all of the traces etched into the proprietary ARM chip in your pi.

Great point.

It is now possible to get a Raspberry Pi equivalent with a processor from Rokchip.

Rokchip's sources are at: https://github.com/rockchip-linux

I find that most stuff from LibreComputer is as open as possible, today.

The Renegade is a pretty good place to start exploring. With Armbian loaded, it's a serviceable personal PC for $35.

The catch is that pre-built Raspberry Pi images won't work for it - because the CPU chip requires different drivers. So it's not a drop-in replacement for various Raspberry Pi recipes. I've built some of those recipes from source code on it, and they work fine, of course.