I tried these from Nix - ArchWiki
06:52:32 jr@fm ~ ⬡ v8.16.0
$ sudo chown -R $USER. /nix/var/nix/{gcroots,profiles}
[sudo] password for jr:
06:52:40 jr@fm ~ ⬡ v8.16.0
$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
06:52:48 jr@fm ~ ⬡ v8.16.0
$ nix-channel --update
unpacking channels...
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
06:52:55 jr@fm ~ ⬡ v8.16.0
$ nix-env -u
warning: Nix search path entry '/nix/var/nix/profiles/per-user/root/channels' does not exist, ignoring
06:53:05 jr@fm ~ ⬡ v8.16.0 6s
$ sudo nix-channel --update
warning: the group 'nixbld' specified in 'build-users-group' does not exist
unpacking channels...
warning: the group 'nixbld' specified in 'build-users-group' does not exist
error: the group 'nixbld' specified in 'build-users-group' does not exist
error: program '/nix/store/6chjfy4j6hjwj5f8zcbbdg02i21x1qsi-nix-2.3.1/bin/nix-env' failed with exit code 1
06:53:06 ✘ jr@fm ~ ⬡ v8.16.0
$
I’ll revisit warning: the group 'nixbld' specified in 'build-users-group' does not exist
later.