Issue with virtualbox guest additions

Hi,

I am a total noob with NixOS
I have install nixos-gnome-23.11.5911.e38d7cb66ea4-x86_64-linux.iso in virtualbox
I am running virtualbox 7.0.12 r15948
I have put Gnome in X11
I have inserted in /etc/nixos/configuration.nix the following :

{
virtualisation.virtualbox.guest.enable = true;
virtualisation.virtualbox.guest.x11 = true;
}

even after reboot and login, it does not resize
what am I missing ?
Thanks