Flake system does not follow `--eval-system`

[roberth]

Describe the bug

Flake system does not follow --eval-system

Steps To Reproduce

$ nix eval .#default.system
"x86_64-linux"

$ nix eval .#default.system --system "aarch64-darwin"
"aarch64-darwin"

$ nix eval .#default.system --eval-system "aarch64-darwin"
"x86_64-linux"

Expected behavior

$ nix eval .#default.system --eval-system "aarch64-darwin"
"x86_64-linux"

nix-env --version output

Additional context

• Added in 2.20, Add eval-system option #4093

Priorities

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