Product Backlog involves the following activities12:

Reducing or eliminating dependencies between Product Backlog items. This helps to increase the flexibility and adaptability of the Product Backlog, and enables the Developers to select the most valuable and feasible items to work on in each Sprint3.

Reviewing the Product Backlog with stakeholders. This helps to ensure that the Product Backlog reflects the needs and expectations of the customers and users, and that the Product Owner receives feedback and input from various perspectives4.

Breaking large Product Backlog items into multiple smaller Product Backlog items. This helps to create a more granular and transparent Product Backlog, and allows the Product Owner to prioritize and refine the items more effectively5.

Ordering the Product Backlog. This helps to communicate the relative importance and urgency of the Product Backlog items, and guides the Developers to select the most valuable items for the next Sprint.

Forecasting the effort of Product Backlog items is not an activity that is explicitly required for managing a Product Backlog. The Product Owner is mainly responsible for maximizing the value of the product, not the effort or cost of development. The effort of Product Backlog items may be estimated by the Developers, but this is not a mandatory practice and it does not affect the ordering of the Product Backlog. References: 1: Product Backlog Management, 2: Managing Products with Agility, 3: Reducing Dependencies, 4: Reviewing theProduct Backlog, 5: Breaking Down Product Backlog Items, : Ordering the Product Backlog, : The Product Owner, : Estimating Product Backlog Items