Explanation
A target value of lightning__FlowScreen in metadata allows for a Lightning web component to be used in guided user experiences to gather input and to automatically generate configuration properties for the Lightning web component. The lightning__FlowScreen target value specifies that the component can be used on a flow screen, which is a type of flow element that displays information and collects user input in a flow. A flow is a guided user experience that can automate business processes and guide users through screens, actions, and decisions. By using the lightning__FlowScreen target value, the developer can expose their Lightning web component as a custom screen component that can be added to any flow screen. The developer can also use the @api decorator to expose public properties of their Lightning web component as configuration properties that can be set in Flow Builder. Flow Builder is a tool that allows the developer to create and modify flows using a drag-and-drop interface. A target value of lightning__FlowScreen does not allow the Lightning web component to replace standard functionality in flows and subflows or to be dragged onto a page in Lightning App Builder, as these are not related to the flow screen target value. Salesforce References: Lightning Web Components Developer Guide: Configure Components for Flows, Lightning Web Components Developer Guide: Communicate with Flow, Lightning Flow Developer Guide: Screen Components Basics