Reporting was always a pain point in Azure DevOps, because people used on SQL Server reporting Services for the on-premise version, missed a similar ability to create custom reports in Azure Dev Ops.
Now you have a nice integration with Power BI and a nice article here that explains how to connect Power BI to your instance and create some basic query. The nice part is that you can use a query that will connect directly with the OData feed, no need to install anything.
Figure 1: Sample OData query that directly connects to your organization account to query for Work Item Data.
I strongly encourage you to experiment with Power BI because is a powerful tool that can create really good report, closing the gap with on-premise version and old Reporting Services.