nixos-config/modules/system/services/server/fileserver/nextcloud/user/default.nix

{ config, lib, ... }:
{
  users = lib.mkIf config.services.nextcloud.enable {
    users.nextcloud = {
      group = "nextcloud";
      extraGroups = [ "nfsShare" ];
      isSystemUser = true;
      uid = 218;
    };
    groups.nextcloud = {};
  };
}