Plenty of newer stuff that is explicitly open like the system 7 and framework stuff also.
> Even in that case, a laptop with Coreboot will still use closed-source components that cannot be trusted,
As does any solution relying on a BIOS.
> If someone steals the device, I cannot see any difference between our 2 setups.
In my setup, if the laptop is stolen, the thief is able to use a limited OS that give them all the functionality they would need while running a locator service in the background, allowing the hardware to be recovered, while preventing access to encrypted data.
It doesn't sound like your setup allows for that.
> However in the case that relies on the internal firmware and TPM to protect the keys, there are more sophisticated hardware attacks against the motherboard,
No matter what, using a BIOS makes you a lot more vulnerable than using any form of secure boot. It's a significantly more vulnerable standard.
