Windows 11 Preview Reveals WinUI 3 Properties Dialog With Dark Mode

Overview

• Community researcher PhantomOfEarth found the hidden modern Properties dialog in Windows 11 preview builds this week, visible when inspecting items in the Recycle Bin.
• The new window is implemented in WinUI 3 and adds dark mode and modern controls instead of the decades‑old Win32 property‑sheet host.
• Microsoft has said it plans to move more Shell surfaces to WinUI and is working on WinUI performance improvements as part of its Windows K2 initiative.
• Many third‑party tools add tabs to the legacy Properties dialog by returning HWND‑based pages through IShellPropSheetExt, so Microsoft needs a 'reverse‑islands' embedding path to avoid breaking those extensions.
• The change appears to be an incremental test with no public rollout date and raises questions about WinUI cold‑start costs and the timing of compatibility fixes to protect users and third‑party software.