√ nix upgrade-nix
[0.0 MiB DL] downloading 'https://github.com/NixOS/nixpkgs/raw/master/nixos/modules/installer/tools/nix-fallback-paths.nix'warning: unknown setting 'signed-binary-caches'
[0.0 MiB DL]
warning: unknown setting 'signed-binary-caches'
replacing old 'nix-2.1.1'
installing 'nix-2.1.1'
building path(s) ‘/nix/store/q37gn45a3ylpjghkfcvnla7hs5yg1jym-user-environment’
error: unsupported builtin function ‘buildenv’
builder for ‘/nix/store/ddq105fnqkda93kdl4p436h96c4fan5c-user-environment.drv’ failed with exit code 1
error: build of ‘/nix/store/ddq105fnqkda93kdl4p436h96c4fan5c-user-environment.drv’ failed
error: program '/nix/store/h180y3n5k1ypxgm1pcvj243qix5j45zz-nix-2.1.1/bin/nix-env' failed with exit code 100