List all installed plugins
After upgrading APEX I found this query useful to review all the plugins I had installed across multiple workspaces and in multiple applications to find ones that needed to be upgraded.
select name ,plugin_type ,version_identifier ,workspace ,application_id ,application_name from APEX_APPL_PLUGINS where workspace not in ('INTERNAL','COM.ORACLE.CUST.REPOSITORY') order by name, workspace, application_id;