Excel - single window, more files

HelloCodeKamil​, 

Since Excel 2013, Microsoft Excel uses a Single Document Interface (SDI) model, meaning each workbook opens in its own top-level window with its own ribbon. This replaced the older Multiple Document Interface (MDI) used in Excel 2010 and earlier. The change was intentional and is part of the core application architecture, so it cannot be reverted through settings. Microsoft’s documented reasons include improved multi-monitor support, better window management within Windows, and improved stability and crash isolation. See: Differences between Excel 2010 and Excel 2013 (Microsoft documentation) https://learn.microsoft.com/office/troubleshoot/excel/differences-between-excel-2010-and-excel-2013 There is currently no option to return to the legacy single-window behavior. As workarounds, you can use View > Arrange All, View > View Side by Side, and View > Switch Windows to manage multiple workbooks more efficiently. If you want Microsoft to consider usability improvements (for example ribbon synchronization or optional window grouping), the appropriate channel is File > Feedback > Send a Suggestion inside Excel, or the Microsoft Feedback Portal at https://feedbackportal.microsoft.com Product changes are driven by telemetry and consolidated feedback rather than forum discussions, so submitting and upvoting structured suggestions there is the most effective approach.