Nix-ld is only used by unpatched executables that use the link loader at /lib or /lib64. If you use for example python from nixpkgs than it will not pick up NIX_LD_LIBRARY_PATH and NIX_LD since these types of binaries are configured to use a glibc from the nix store.

• https://github.com/nix-community/nix-ld/blob/bc1a7a1b88589bfd26846fc5341fe44fc73b3fbd/README.md?plain=1#L164

Ah, I guess that's why I've seen folks recommend just having uv install the python interpreter as well, so everything python uses the same link loder from nix-ld.