Blurry Windows dialog boxes and system windows at 125% DPI scaling in Windows 11 26H2

For Device Manager and other MMC snap-ins, test a per-application DPI compatibility override on C:\Windows\System32\mmc.exe; this can replace blurry bitmap enlargement with sharper, potentially smaller UI.

Test the MMC compatibility override

This change is reversible, but it can make controls too small or cause clipping or overlap.

1. Close Device Manager and every MMC console.
2. Open File Explorer and browse to: C:\Windows\System32
3. Right-click mmc.exe → Properties → Compatibility.
4. Select Change high DPI settings.
5. Enable Override high DPI scaling behavior.
6. Choose Application from the Scaling performed by list.
7. Select OK → Apply → OK.
8. Reopen Device Manager and inspect its main window and adapter-property dialogs at 125%.

Microsoft documents mmc.exe as DPI-unaware and states that Windows bitmap-scales it at high DPI, which can make it fuzzy at 125% and 150%. Microsoft also documents the per-application compatibility shim for preventing that bitmap scaling, with the warning that it can introduce small, clipped, or overlapping content.^1^

Because MMC is a shared host, this setting can affect Device Manager and every other MMC snap-in. If the result is worse, return to the same dialog and clear Override high DPI scaling behavior.

What the test results indicate

Your results are characteristic of DPI-unaware bitmap scaling:

• At 100%, the application renders at its native 96-DPI size, so no enlargement is required.
• At 125% or 150%, Windows enlarges the completed application bitmap, including text, icons, controls, and window borders.
• Fractional bitmap scaling is particularly prone to visible softness. Microsoft identifies 125% as the scale where fuzziness in DPI-unaware applications is generally most noticeable.^1^

Per-Monitor V2 applications avoid this bitmap stretching and render the appropriate assets and controls for the current DPI instead.^2^

The fact that sysdm.cpl and mmsys.cpl remain sharp does not contradict this diagnosis: individual processes, dialogs, and window trees can use different DPI-awareness modes.

Other affected dialogs

The MMC override addresses MMC-hosted windows only. It will not necessarily correct:

• Outlook profile dialogs
• Network and Wi-Fi property dialogs
• Other dialogs hosted through rundll32.exe

Do not apply a blanket override to rundll32.exe solely from its process-level classification. It hosts many different components, and the awareness of that executable alone does not establish the DPI context of every hosted dialog. If testing it, use the same reversible procedure, document which exact dialog changes, and remove the override if other Control Panel dialogs develop sizing or layout problems.

There is no universally safe global setting that forces every legacy system component to become DPI-aware. Remaining practical choices are:

• Keep 125% and use targeted compatibility overrides where they improve a specific executable.
• Use 100% scaling and enlarge text separately through Settings → Accessibility → Text size.
• Wait for the affected component to be updated for Per-Monitor V2 DPI awareness.

Windows 11 26H2 status and reporting

The detailed public 26H2 release-health content currently shown does not display a matching MMC/rundll32 blurry-dialog entry or an applicable Known Issue Rollback. Its listed October fixes concern other issues, so those KIR packages should not be installed for this symptom.^3^

Report the build-specific behavior through Feedback Hub:

1. Open Feedback Hub and search for existing reports containing 26H2 blurry dialogs 125% MMC.
2. Upvote a matching report or create a new one.
3. Include build 26300.9711, resolution 1920 × 1080, screenshots at 100% and 125%, affected dialog names, and the measured DPI-awareness results.
4. State whether the MMC Application override makes Device Manager sharp and whether it introduces clipping.

Microsoft documents searching for an existing report and then upvoting it or submitting a new report through Feedback Hub.^4^

References

1. Fixing blurry text in Windows for IT Professionals
2. High DPI Desktop Application Development on Windows
3. Windows 11, version 26H2 known issues and notifications
4. Diagnostics, feedback, and privacy in Windows | Microsoft Support