Hi, thank you for the report! This is definitely a problem.
It seems that the Linux kernel already started up so this is not a bootloader problem but rather a problem with the Linux kernel. There have been lots and LOTS of amdgpudrmfb changes in the Linux kernel lately - but our GuixSD release is pretty old. There should be a new release soon - the 0.14.0 release is from Dec 2017 and the Linux kernel from back then had some problem modesetting AMD cards. See also https://apple.stackexchange.com/questions/211260/grub-2-error-fb-switching-to-radeondrmfb-from-efi-vga As a workaround, (1) Wait until the grub menu shows up (2) Press e (3) Go to the end of the line which says "linux" (4) Add a space (5) Add nomodeset (6) Press F10
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