To make a custom Lightning component available for selection in a utility bar, it must be explicitly configured for that target. For a Lightning Web Component (LWC), the developer must include lightningUtilityBar in the component's js-meta.xml configuration file. For an Aura component, it must implement the flexipage:availableForAllPageTypes interface. This configuration acts as a "tag," signaling to the Lightning App Builder that the component is compatible with and can be added to a utility bar within the App Manager.

A. Tagging a component for use on record pages makes it available only on record detail pages, not in the utility bar.

B. This is too general. A component needs a specific target (e.g., utility bar, record page) to appear in the Lightning App Builder for that context.

D. The App Manager is the user interface for configuring an app's utility bar, but the component itself is not tagged for the App Manager tool.

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1. Salesforce Lightning Web Components Developer Guide: Configure a Component for Different Page Types. The documentation specifies the tag for the component's configuration file. It explicitly lists lightningUtilityBar as the target value that "Enables a component to be used in a utility bar."

2. Salesforce Aura Components Developer Guide: Component Configuration for Lightning App Builder. This guide states, "To make your component usable in a utility bar, implement the flexipage:availableForAllPageTypes interface." This interface makes the component appear in the Lightning App Builder for all page types, including the utility bar.

3. Salesforce Help & Training: Add a Utility Bar to Lightning Apps. This document explains the process of adding items to a utility bar and notes that you can add "Custom components that your developer has configured to be used in a utility bar," confirming that a specific configuration is required.