toybox is likely intentionally very small and intended to provide only the basic functionality. The pciutils package has a more full-fledged version of lspci:
$ nix-shell -p toybox --run lspci
03:00.0 : (rev 1a)
00:02.7 : (rev 00)
<...>
$ nix-shell -p pciutils --run lspci
00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne Root Complex
00:00.2 IOMMU: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne IOMMU
<...>