Running nixos-install from SOQuartz SD image gives 'flakes' is disabled error

[msgilligan]

When I try to use the SoQuartz SD Image to install NixOS to NVMe, I get the following error:

error: experimental Nix feature 'flakes' is disabled; use '--extra-experimental-features flakes' to override

Using sudo NIX_CONFIG="experimental-features = nix-command flakes" nixos-install seems to work-around the problem, but when installing to NVMe from other NixOS installer images this isn't required. It seems like installers created with this image require flakes without flakes being enabled.

Normally, to enable flakes I would edit /etc/nixos/configuration.nix (NixOS) or /etc/nix/nix.conf (Nix package manager only), but the first one didn't exist and the second strongly discouraged modification.