GrapheneOS requires the bootloader be locked for a complete install. But it does require the bootloader be unlockable and support yellowboot.
GrapheneOS, Android, and android based OSs, are all linux distros.
Correct and correct.
I think most readers are able to understand what I mean when I say Linux.
Given that Android doesn't respect me as a user at all, that it sandboxes me out of my own system, I can maybe regard it as a Linux perhaps, but as it ships: it's never my Linux. It's Google's Linux. Running on my device.