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.

You don't need any of that to understand how x86 or the OS works. Realistically you can do the entire learning with QEMU/VM and not be restricted by the hardware at all?

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.

It really depend on what you want to do - Linux distro on x86 is IMHO good start, but of course its not the only option - there are now some reasonably open arm devices (including an atm laptop) from pine, there is the very open Tales workstation running on Power & RiscV showing up everywhere.

Why do people make these kinds of comments? Talos isn’t showing up anywhere, and even during the Kickstarter it was more than $3000 for just a motherboard.

As an example of what is available ? And these do get used - for example as a desktop: https://m.youtube.com/watch?v=ktSwuF32ywM

Also they seem to have released a cheaper micro ATX board: https://www.raptorcs.com/BB/