Previously, in the classic UI, there was an Additional Users field alongside the Project Primary Contact field. This field was removed with the New UX. My client, Husch Blackwell, has a very specific use case detailed in ticket #59852. We are requesting to bring this field back.
Not every user needs to be a PPC, but they might still benefit from receiving notifications and updates about the project and they are interested in this for reporting purposes. Additionally, this field could support roles like authors or reviewers who are actively involved in the project.