To fix a slow-loading Power BI report with million of rows and many visuals, use the Performance Analyzer (View ribbon) in Desktop to identify bottlenecks. The analyzer breaks down loading times into DAX query, visual display, and other times for each visual. Focus on optimizing DAX measures, reducing visuals per page (aim for 8-10), implementing incremental refresh, and using aggregated tables to improve performance. Reference: https://learn.microsoft.com/en-us/power-bi/create-reports/performance-analyzer