
The configuration { services.openssh.enable = true; services.openssh.forwardX11 = false; } caused programs.ssh.setXAuthLocation to be set to false, which was not the intent. The intent is that programs.ssh.setXAuthLocation should be automatically enabled if needed or if xauth is already available.
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at http://nixos.org/nixos and in the manual in doc/manual.