I'm not having trouble building Nyxt today using Guix commit 9703a51. Perhaps OP can try to build it again now.
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OS: Guix System 9703a51048fbc1d322595d676ff0d63b1eb89304 x86_64
Host: OptiPlex 9020 00
Kernel: 5.12.8-gnu
Uptime: 8 days, 7 hours, 22 mins
Packages: 92 (guix-system), 108 (guix-user)
Shell: bash 5.0.16
Resolution: 1920x1080
DE: GNOME
Theme: Adwaita [GTK2/3]
Icons: Adwaita [GTK2/3]
Terminal: kitty
CPU: Intel i5-4570 (4) @ 3.600GHz
GPU: Intel HD Graphics
GPU: AMD ATI Radeon HD 8490 / R5 235X OEM
Memory: 4903MiB / 7869MiB
Christopher Howard