Refer to the product documentation: https://enterprise.arcgis.com/en/portal/latest/administer/windows/administer-a-federated-server.htm#ESRI_SECTION3_A4EFC90DD8BB475A9636DC10E3013295.
For federated servers with restricted publishing, portal members with publisher privileges are not granted to have publishing access to the server by default. Instead, publisher access to the server is controlled by a group named [federated server name]_Publishers or the item [federated server name]_Publishers. In order to gain publisher privilege to the server, the portal member must be either a member of the [federated server name]_Publishers or a member of a group where the [federated server name]_Publishers item has been shared with.