The "Add" and "Design" tab in the new Page Editor
The new HubSpot drag and drop page editor, where you can add/remove modules and make layout changes directly at the page level is currently only supported on coded templates that include dnd_areas.
Act2 however are drag and drop (not coded) templates and making layout changes, like adding modules, columns, etc, is only possible at the template level, in the Design Tools.
You can read more about the two types of templates here:
Also, to make a better idea, please read our documentation here: https://neambo.com/support/act21
We have not intentionally disabled adding new modules in the page editor. It’s just not possible to do that with drag-and-drop templates, except one module at the time in a single column using Flexible Columns.