error:
       … while evaluating the attribute 'optionalValue.value'
         at «git+https://github.com/NixOS/nixpkgs?ref=nixpkgs-unstable&rev=335f0738cb2fa9708f3f428e39d2eae975d1338d&shallow=1»/lib/modules.nix:1312:5:
         1311|
         1312|     optionalValue = if isDefined then { value = mergedValue; } else { };
             |     ^
         1313|   };

       … while evaluating a branch condition
         at «git+https://github.com/NixOS/nixpkgs?ref=nixpkgs-unstable&rev=335f0738cb2fa9708f3f428e39d2eae975d1338d&shallow=1»/lib/modules.nix:1312:21:
         1311|
         1312|     optionalValue = if isDefined then { value = mergedValue; } else { };
             |                     ^
         1313|   };

       … while evaluating definitions from `/nix/store/xfg4bws749i95jvnxhymxmfwailzk38q-source/modules/transposition.nix':

       … while evaluating definitions from `/nix/store/bfvim3d54a9b1k6av0i54xjv6hzlmgf5-source/flake.nix, via option perSystem':

       … while evaluating definitions from `/nix/store/xfg4bws749i95jvnxhymxmfwailzk38q-source/modules/transposition.nix':

       … while evaluating definitions from `/nix/store/bfvim3d54a9b1k6av0i54xjv6hzlmgf5-source/nix/packages/flake-module.nix, via option perSystem':

       … while evaluating definitions from `/nix/store/xfg4bws749i95jvnxhymxmfwailzk38q-source/modules/transposition.nix':

       … while evaluating definitions from `/nix/store/bfvim3d54a9b1k6av0i54xjv6hzlmgf5-source/nix/packages/flake-module.nix, via option perSystem':

       … while evaluating the module argument `pkgs' in ":anon-13:anon-1":

       … noting that argument `pkgs` is not externally provided, so querying `_module.args` instead, requiring `config`

       … while evaluating definitions from `/nix/store/xfg4bws749i95jvnxhymxmfwailzk38q-source/modules/transposition.nix':

       … while evaluating definitions from `/nix/store/bfvim3d54a9b1k6av0i54xjv6hzlmgf5-source/flake.nix, via option perSystem':

       … while evaluating definitions from `/nix/store/xfg4bws749i95jvnxhymxmfwailzk38q-source/modules/transposition.nix':

       … while evaluating definitions from `/nix/store/bfvim3d54a9b1k6av0i54xjv6hzlmgf5-source/nix/devShells/flake-module.nix, via option perSystem':

       … while evaluating the module argument `pkgs' in ":anon-14:anon-1":

       … noting that argument `pkgs` is not externally provided, so querying `_module.args` instead, requiring `config`

       … while evaluating definitions from `/nix/store/bfvim3d54a9b1k6av0i54xjv6hzlmgf5-source/flake.nix, via option perSystem':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: Nixpkgs 26.11 has dropped support for x86_64-darwin.

       The 26.05 stable branch still supports x86_64-darwin, and will
       receive security fixes until the end of 2026. If you use channels,
       you can switch to 26.05 as follows:

           $ sudo nix-channel --add https://nixos.org/channels/nixpkgs-26.05-darwin nixpkgs
           $ sudo nix-channel --update

       If this doesn’t work, you may need to run:

           # Lack of sudo is deliberate:
           $ nix-channel --remove nixpkgs

       If you use flakes, switch your flake input:

           inputs.nixpkgs = {
             url = "github:NixOS/nixpkgs/nixpkgs-26.05-darwin";
           };

       See the release notes for more information and alternatives:

         https://nixos.org/manual/nixpkgs/unstable/release-notes#x86_64-darwin-26.11