In short, this DLL acts as a bridge. When a developer tries to deploy a test app, or a user tries to sideload an app, the system calls this DLL to check permissions and unlock the necessary capabilities.
This specific DLL is associated with the (Application Model) framework. Its primary function is to manage "unlocking" features or capabilities for Windows applications, particularly those within the Universal Windows Platform (UWP) or related to modern app deployment. api-ms-win-appmodel-unlock-l1-1-0.dll
Many apps require specific runtime libraries to interpret these DLL calls. In short, this DLL acts as a bridge