Wrong wiki. Use https://wiki.nixos.org/wiki/Visual_Studio_Code#Use_VS_Code_extensions_without_additional_configuration which mentions
Note:
︎
buildFHSEnvallows for ease-of-use at the cost of impurity, non-reproducibility, and denied root access (you cannot usesudoin.fhspackages, also see [1])
Though even that note can be improved, because I have no idea what “ease of use” means here.