Who is accountable for creating a valuable and usable Increment each Sprint?

Scrum

According to the Scrum Guide 2020, the entire Scrum Team is accountable for creating a valuable, useful Increment every Sprint1234. This includes the Developers, the Product Owner, and the Scrum Master4. The Developers are committed to creating any aspect of a usable Increment each Sprint12, while the Product Owner is accountable for maximizing the value of the product resulting from the work of the Scrum Team12. The Scrum Master fosters an environment where the Scrum Team can work effectively1.