There are two reasons why the space option would not appear. One, Space might be disabled in the "Add Content" of your Global Settings, and two, you're at your max usage for spaces available in your digital workplace.
You can find the global settings by going to your Control Panel, and once on the global settings, search for the "Add Content" section, and confirm if the checkbox next to Space, is checked.
If that is checked off, then you would need to reach out to Customer Success Manager to confirm the amount of spaces that you're allowed and to check if you're at the max allowed spaces or not. If your customer success rep, please send a ticket to email@example.com, and we can route your ticket accordingly.