I recently upgraded the Power BI Report Server by following this article Upgrade Power BI Report Server to the latest May 2025 update, and the upgrade has been done sucessfully, but after upgrade all dashboard with "Direct Mode" is not currently working and show this error.
We couldn't connect to the Analysis Services server. Make sure you've entered the connection string correctly.

This issue is only found for all dahshboards file, the paginated report is working properly.