The Product Owner orders the Product Backlog items according to various criteria, such as:

The value of Product Backlog items. The Product Owner aims to maximize the value of the product and the work of the Scrum Team. Therefore, they prioritize the items that deliver the most value to the stakeholders and the users, considering factors such as customer satisfaction, market share, revenue, social impact, etc.

The dependencies between Product Backlog items. The Product Owner tries to minimize the dependencies between items, as they may create complexity, uncertainty, and risk. Therefore, they order the items in a way that reduces or eliminates the dependencies, or resolves them as early as possible.

The dependencies to other products. The Product Owner also considers the dependencies that the product has to other products, such as platforms, frameworks, libraries, services, etc. Therefore, they order the items in a way that aligns with the availability and compatibility of those products.

References:

Scrum Guide 2020, page 11: “The Product Owner is accountable for effective Product Backlog management, which includes … ordering Product Backlog items; and, ensuring that the Product Backlog is transparent, visible and understood.”

Scrum Guide 2020, page 11: “The ordering of the items in the Product Backlog is the sole responsibility of the Product Owner. They order Product Backlog items to best achieve goals and missions.”

Scrum Guide 2020, page 11: “Higher ordered Product Backlog items are clearer and more refined than lower ordered ones.”