No, The Product Owner should never act in the Scrum Master role. These two roles have conflicting goals and should not be merged.
Disadvantages: There is a huge conflict of interest because the Scrum Master and Product Owner roles have conflicting goals. The Scrum Master should never be responsible for delivery; that is the Product Owner’s main goal. It’s a conflict between business needs and team self-awareness. It’s about balancing long-term versus short-term improvements and results.
Result: In most cases, the role of Scrum Master is neglected and the Product Owner controls everything. Such a team usually lacks any deep Scrum understanding and self-organization. All scrum ceremonies will be more of a status reporting meeting.