The primary focus of a lessons learned exercise following a successful response to a cybersecurity incident is to evaluate how the incident management processes were executed, and to identify the strengths, weaknesses, best practices, and improvement opportunities for future incidents. A lessons learned exercise is not meant to determine the root cause, the attack vectors, or the recovery time of the incident, but rather to assess the performance and effectiveness of the incident response team and the incident response plan.
References: The CISM Review Manual 2023 states that "post-incident reviews are an essential part of the incident response process" and that "they provide an opportunity to assess the performance of the incident response team, identify areas for improvement, and document lessons learned and best practices" (p. 191).
The CISM Review Questions, Answers & Explanations Manual 2023 also provides the following rationale for this answer: "How incident management processes were executed is the correct answer because it is the primary focus of a lessons learned exercise, which aims to evaluate the incident response capability and to implement corrective actions and improvement plans" (p. 97). Additionally, the Cybersecurity Incident Response Exercise Guidance article from the ISACA Journal 2022 states that "The AAR [after-action review] should include the date and time of the exercise, a list of participants, scenario descriptions, findings (generic and specific), observations with recommendations, lessons learned and an evaluation of the exercise (strengths, weaknesses, lessons learned)" (p. 3)1