You can check https://experienceleague.adobe.com/docs/experience-manager-cloud-service/content/assets/admin/xmp-metadata.html?lang=en to see if you can avoid implementing com.day.cq.dam.api.handler.xmp.XMPWriteBackOption in your custom code.If this is not possible, contact Adobe Support Team.
Although PostgreSQL is not supported in AEM 6.5 and above, as mentioned in https://experienceleague.adobe.com/docs/experience-manager-65/deploying/deploying/rdbms-support-in-aem.html?lang=en.But you can still check with Adobe Support Team if this is true for AEM as Cloud. For a list of supported dat...
https://experienceleague.adobe.com/docs/experience-manager-65/assets/administer/config-smart-tagging.html?lang=en for integrating Smart tagging with AEM.