A developer needs to make a custom Lightning Web Component available in the Salesforce Classic user interface. Which approach can be used to accomplish this?

Wrapping an LWC in an Aura Component is a pattern for exposing LWC to other Aura components, typically within Lightning Experience, and does not inherently make the component available in Salesforce Classic without the use of Lightning Out applied to the Aura component.

Lightning Web Components cannot be directly embedded into Visualforce Components because they are based on different underlying frameworks and rendering engines, requiring a bridging mechanism like Lightning Out.

Lightning Out is a feature designed to embed Lightning Components (both Aura and LWC) into external web applications, including Salesforce Classic Visualforce pages, by providing the necessary JavaScript library to bootstrap the Lightning runtime. This allows modern components to be rendered in older UI contexts.

While a Visualforce page is involved, simply using a custom controller to 'invoke' an LWC is not the defined mechanism; Lightning Out provides the specific framework and JavaScript library for embedding LWCs.