Earlier quoted context omitted.
Most of the issues you list should not be a problem if you use a Linux distro on a fairly standard pc/laptop. Pretty much all inside it is open for you to look into and change as needed.
At the OS level sure. Its still running on a completely non-free / hardly hackable platform though riddled with all sorts of backdoors and other curiosities. I'm aware of things like coreboot / libreboot, but support is even more limited there and porting involves a deep understanding of the x86 platform in my brief experience.
At some institutions they teach how OS work by students implementing Pintos, a full x86 OS.
In my first year I had to build a full raspberry pi emulator from scratch and then code an assembler for it. These programs would then run natively on the raspberry pi. People wouldn't even touch the hardware until much, much later into the project when the emulator has confirmed to be working.
I disagree with the view that you need a full FOSS hardware to understand a platform. You can do a lot with a VM/QEMU.