I can only find:
nix-repl> config.systemd.network
{
config = { ... };
enable = true;
links = { ... };
netdevs = «repeated»;
networks = { ... };
units = { ... };
wait-online = { ... };
}

nix-repl> config.systemd.network.networks
{
"99-ethernet-default-dhcp" = { ... };
"99-wireless-client-dhcp" = { ... };
}

I'm not getting services..

Loading installable ''...
Added 13 variables.
baseModules, config, extendModules, extraModules, flake, lib, moduleType, modules, modulesPath, noUserModules, options, pkgs, utils
nix-repl> services
error: undefined variable 'services'
       at «string»:1:1:
            1| services
             | ^

nix-repl>