I think You need to set the Items property of the combo box to a formula that retrieves the person field values from the list, and also set the DisplayFields property to show the relevant information, such as DisplayName or Email.
For example, you can use this formula in the Items property of the combo box:
Distinct('YourSPList'.PersonField, PersonField.DisplayName)This will return a list of distinct display names from the person field in your SharePoint list. You can also use other properties of the person field, such as Claims, Department, JobTitle, etc.
Then, you can use this formula in the DisplayFields property of the combo box:
This will show the display name of the person in the combo box. You can also add other fields, such as Email, JobTitle, etc.