Direct the focus of optimization on work items, e.g. tasks, problems, process steps, instead of the people. That means metrics also need to focus on work items, not on people.
Everybody already experienced a few times in their life that it is totally possible that everybody is busy to the point of being overworked but the work gets done slower and slower.
One could ask themselves, why is that? And what is more important? Is it better that everybody is busy or would it be better if more work gets done?
Usually in comparison it should be clear the second point is much more important: work needs to get done.
But to get there one cannot track indirect metrics like utilization of employees. Instead one needs to track work item related metrics like how long a task stays work in progress. And one needs to make visible when tasks get stuck so the team can analyse together why it got stuck and how this could be avoided the next time.
Typical activities for managing flow are:
Check out these great links which can help you dive a little deeper into running the Manage Flow practice with your team, customers or stakeholders.