Why I can't use Gnome environment?

Why I can't use Gnome environment?
I applied all steps from this tutorial

Zorin didn't give me Gnome on the list?

What can I do to switch to Gnome environment?

If you are using Core version of Zorin then it already uses Gnome enviroment. The guide shows Ubuntu 21.04, but Zorin 16 is build upon 20.04.

As it says in the guide: Make sure you have Ubuntu 21.04 installed.

and down in the text it says: If you really want to get a proper GNOME 40 experience, try with Fedora 34, or install the packages via Arch Linux.