Split application binary into modules.
When enabled, Unity splits up the player executable and data into modules:
APK: Generates an APK that consists only of the executable (Java and Native) code (~10MB), and the data for the first scene. Unity serializes the application data separately in an APK Expansion File (.obb). For more information, refer to APK expansion files.
AAB: Generates an AAB that contains a base module and one or more asset packs. The base module contains the executable (Java and Native) code (~10MB), and the data for the first scene. Asset packs contain the rest of the application data. For more information, refer to Asset packs in Unity.