It seems that you did a multi-user w/ daemon installation. I am aware that a functioning guide is here
so get nix using the darwing unencrypted label
sh <(curl -L https://nixos.org/nix/install) --darwin-use-unencrypted-nix-store-volume
sudo nano /etc/nix/nix.conf file, by adding IOHK's binaries:
build-users-group = nixbld
substituters = https://hydra.iohk.io https://iohk.cachix.org https://cache.nixos.org/
trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= iohk.cachix.org-1:DpRUyj7h7V830dp/i6Nti+NEO2/nhblbov/8MW7Rqoo= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
system = x86_64-darwin
extra-platforms = x86_64-darwin aarch64-darwin
sandbox = false
extra-sandbox-paths = /System/Library/Frameworks /System/Library/PrivateFrameworks /usr/lib /private/tmp /private/var/tmp /usr/bin/env
experimental-features = nix-command
extra-experimental-features = flakes
reboot and you should be good to go.
note I am no Nix expert nut if the problem persists then you might need to completely uninstall Nix first, which is not so trivial.