The user is experiencing significant issues with the new Outlook application after a recent update on June 26th, 2026. Initially, the application functions correctly, allowing access to settings, closing the window, and using the file menu. However, upon attempting to reply to an email, the entire interface freezes. Subsequently, the settings menu, the close button, and the file pull-downs become unresponsive. Copilot has identified this behavior as a known issue within the Windows Insider Beta program, specifically linked to a WebView2 runtime mismatch. The problematic operating system build is identified as OS build 26220.8754. This build is documented to contain a regression in the WinUI window-frame dispatch. Therefore, the problem lies with Windows itself, not directly with the Outlook application. There is no immediate local solution available to fix this. The user must wait for Microsoft to release a patch for the identified regression. Rolling back to a previous Insider build has been confirmed to resolve the problem. Remaining on the current build, 26220.8754, will prevent the Outlook window from closing using the "X" button.