Profile /nix/.../per-user/mark/profile is incompatible with nix-env

[mark999]

I want to update nix.

$ nix-env --install --attr nixpkgs.nix

error: profile ‘/nix/var/nix/profiles/per-user/mark/profile’ is incompatible with ‘nix-env’; please use ‘nix profile’ instead

$ nix profile upgrade nix

warning: Found package ‘nix’, but it was not installed from a flake, so it can’t be checked for upgrades!
warning: Found some packages but none of them could be upgraded.

$ nix-env --upgrade

(same error as nix-env –install …)

$ nix --version

nix (Nix) 2.25.3

I have read

Reinstall Nix: nix-env incompatibility

I have a system on which Nix was installed using apt install nix-bin. I am attempting to reinstall Nix using the official install script (sh <(curl -L https://nixos.org/nix/install) --daemon). I removed Nix using apt remove nix*, but when I run the install script I get an error: error: profile ‘/nix/var/nix/profiles/default’ is incompatible with ‘nix-env’; please use ‘nix profile’ instead. I understand why this is happening - I believe it is occurring on line 924 of install-multi-user of the…

However the error they encounter involves the default profile, while for me the listed profile is the same as ~/.nix-profile. They’re told to delete default, but I assume that would be bad for me. What to do?