For what it is worth, I'm having the same error when I try to use Internet Recovery on a 2018 15" Macbook Pro to install Big Sur. I can cleanly install Catalina using a bootable USB created via the Terminal, but when I upgrade to Big Sur, the upgrade fails and leaves the machine in an unbootable state. From there, if I try to use internet recovery to install Big Sur it also fails. At this point I've probably performed the installation process a dozen times with a few variations over the last several days to no avail. Interestingly, I also tried to create a bootable Big Sur USB install drive using Apple's instructions, but the media creation fails at the end when trying to "bless" the drive, and ultimately the drive isn't bootable. It almost seems like there's something wrong with the Big Sur installer that's currently hosted on Apple's servers... but I can't imagine how that would happen and then go largely unnoticed for any significant period of time.