Not true about Android at least — there is secure boot where the bootloader will snitch on you if you unlock it, and you can't do anything about it because the

Not true about Android at least — there is secure boot where the bootloader will snitch on you if you unlock it, and you can't do anything about it because the attestation happens in a trusted execution environment, a hypervisor with higher privileges than the OS kernel, that you never get to unlock.