To create an engaging user interface in a Mendix app, what main source is suggested?

The primary source recommended for creating an engaging user interface in a Mendix app is the Atlas UI site. The Atlas UI is specifically designed to provide guidance and resources that align with Mendix's best practices for building user interfaces. It includes design standards, component libraries, and best practice examples that help developers craft user experiences that are not only visually appealing but also consistent and user-friendly.

Utilizing the Atlas UI site allows developers to access the latest design guidelines and patterns that have been curated to work seamlessly within the Mendix environment. This ensures that the applications they build meet both user expectations and technical standards.

While project documentation, developer community advice, and online tutorials may provide helpful insights and information, they do not specifically focus on the UI design principles that the Atlas site offers. Therefore, relying on the Atlas UI site is the best approach for enhancing the user interface in Mendix applications.