Which of the following could be categorized as an external event affecting operational risk?

The identification of supplier bankruptcy as an external event affecting operational risk is grounded in the nature of operational risk itself, which encompasses risks arising from internal processes, people, and systems as well as external factors. Supplier bankruptcy is an event that originates outside of the organization, impacting the company's ability to secure necessary goods or services for its operations. This situation can lead to supply chain disruptions, increased costs, and potential reputational damage, all of which directly affect the operational performance of the business.

In contrast, the other options represent internal issues. Outdated company policies, employee turnover, and inadequate training programs are all based on internal practices and situations that can impact operations but do not stem from external sources. They reflect how an organization manages its internal processes rather than challenges it faces from the external environment. Thus, supplier bankruptcy distinctly aligns as an external risk factor in this context.