Basically, Dynamics 365 Customer Engagement is a Power Apps Model-driven app. They both use the same user interface, design tools, and base system. Both can manage accounts, contacts, leads, opportunities, and can be extended. The main difference is that Dynamics 365 Customer Engagement has more features already baked in and has a longer history. Dynamics 365 CE has a whole collection of 3rd party add-ons that have been developed for it prior to the Power Platform being released. So you might consider the Power Apps Model-driven database to be a stripped down version of the Dynamics 365 CE database.

Features that are in both systems:

• Security
• Cloud Hosting Available
• Customizable
• Workflow
• Auditing
• Email Integration
• Data Management (Import/Export)
• Add-ons from MS App Source
• Dashboard and Reporting
• Web application & Mobile Friendly

Features are that are only for Dynamics 365 Customer Engagement:

• On-Premise Installation
• Outlook Integration
• Document Management (Sharepoint Integration)
• Exclusive Add-ons from MS App Source
• Product Catalog
• Case/Service Management
• Intelligence Features (Relationship assistant, Email engagement, Connection Insights)