No More Form type (Main Form – Interactive Experience and Mobile – Express)

Yes.
Before V 9.0 We had 6 Form types
Main Form
Mobile – Express 
Quick View Form
Quick Create Form
Card Form
Main Form – Interactive Experience

In D365 v 9.0.
We have only Four forms types

Main Form
Quick View Form
Quick Create Form
Card Form

With new UUI – Unified user interface,  Same for type can be rendered on Web and Customer Service hub.

Unified User interface is smart enough to load form (Form Type – Main form) and its control, also it can load custom control if any.

All customization tasks for the Customer Service Hub must be done in the Microsoft Dynamics 365 web application.

Microsoft Developers guide Describe more in details here