In most of the scenarios the SQL based reports are re-developed in fetch XML. But there are scenarios where fetch XML is not successful. In these scenarios following are some of my suggestions:
1. Power BI (online) : Develop the reports using power BI. Power BI is very flexible tool. If you are accessing data directly from D365, this will help you to maintain the data access privilege as defined in D365. Users can define complex reports by themselves and these reports can be accessed from D365 directly.
Power BI reports and dashboards can be accessed via mobile app too.
If data-models / cubes are designed once, further report designing can happen with low-code / no-code. Most of the times drag and drop with rich GUI
2. Using Data Export Service: You will have data in SQL. You can user SSRS, SSAS or any other BI tool in connection with SQL. The data access privileges are ignored while accessing reports (this is treated as raw data). Reports needs to be accessed from outside D365.
Mobility option depends on the third-party BI tool (if any).
If SSRS is chosen, any new / modification in any report will be driven by custom code.