Explanation

Box 1: Set the test environment security group to TestSG and assign test users the app security role.
PowerApps apps use role-based security for sharing. The fundamental concept in role-based security is that a security role contains privileges that define a set of actions that can be performed within the app. All app users must be assigned to one or more predefined or custom roles.
Box 2: Assign the manager the app security role.
Box 3: Set the production environment security group to TestSG
Box 4: Add all users in the department to the TestSG security group.
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/model-driven-apps/share-model-driven-app