GNU forked Libreboot?
They forked Libreboot, due to disagreement with Libreboot’s Binary Blob Reduction Policy. This is a pragmatic policy, enacted in November 2022, to increase the number of coreboot users by increasing the amount of hardware supported in Libreboot. Libreboot’s Freedom Status page describes in great detail, how that policy is implemented - the last few Libreboot releases have vastly expanded the list of hardware supported, which you can read here.