PMP Practice: Distinguish various options to lead various team members and stakeholders

Tala Reyes-Aquino is leading an agile development team at Fractal Horizon Labs, a mobile gaming startup. During the sprint retrospective, several developers express frustration that their creative input on game mechanics is being dismissed by the lead designer, who insists on making all final decisions without team discussion. The team's velocity has dropped 35% over the past two sprints, and two developers mention they are considering leaving. The lead designer, a highly skilled veteran hired six months ago, believes their approach ensures quality and consistency. Tala has already confirmed with the product owner that collaborative design decisions are encouraged and align with the company's culture. What should Tala do to restore team motivation and engagement?