RHI Resolution Mismatch in Borderless/Fullscreen on Windows 11

Development Programming & Scripting UI
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Body: I am observing a consistent discrepancy between GameUserSettings target resolution and GetViewportSize / GetScreenResolution reported values on my machine.

Observed Behavior: Target: 2560x1440 Reported: 2554x1440

Analysis: This appears to be an issue in how the Slate RHI communicates with the Windows DWM (Desktop Window Manager) on specific display profiles. The engine is consistently reporting the ‘Client Area’ reserved by the OS composition layer rather than the physical backbuffer resolution.

Reproduction:

  1. Create a blank project.

  2. Create a Widget querying GetScreenResolution and GetViewportSize.

  3. Launch in Standalone/Fullscreen on a 1440p monitor.

  4. Result: The reported resolution does not match the set resolution in GameUserSettings.

Is this a known behavior with the current Slate RHI implementation in UE 5.x, and are there any recommended workarounds beyond manual resolution clamping?