Upgrading Docebo from version 3.6 to version 4 the new "data aggregation" report type is missing. To activate it siply launch this simple query:
INSERT INTO `learning_report` (`id_report`, `report_name`, `class_name`, `file_name`, `use_user_selection`, `enabled`) VALUES
(5, 'aggregate_report', 'Report_Aggregate', 'class.report_aggregate.php', 'true', 1);
If you are installing from scratch everything is ok.