What is known about Microsoft’s optional Windows 11 update KB5120998, released on August 27, 2026, including the affected versions and builds (25H2 Build 26200.9278 and 24H2 Build 26100.9278), the major features it introduces such as a resizable Start menu, movable Taskbar, and d

KB5120998 is an optional, non-security Windows 11 preview update released August 27 for all editions of 25H2 (OS Build 26200.9278) and 24H2 (OS Build 26100.9278). It delivers notable interface customizations, but some installations have suffered cursor-personalization regressions and other visual problems. 1

• What it adds: Microsoft documents Start-menu sizing controls and taskbar placement at the top, bottom, left, or right screen edge. The preview also changes Search to reduce its prominence/clutter. 1

• Cursor issue: Microsoft’s release-health page now has a formal reported Known Issue for KB5120998—not merely an informal acknowledgement. It says custom cursor settings and cursor animations can intermittently revert. 2 User reports additionally describe pointers becoming abnormally large or small, reverting to white/default colors and other custom settings, or disappearing; these more detailed symptoms are reported externally rather than all being explicitly confirmed by Microsoft. 3

• Other reported effects: Some affected users report their desktop background resets to a black/blank state, and there are reports of font-rendering defects. These appear to be user and press reports, not yet fully enumerated in Microsoft’s advisory. 3

• Microsoft’s status: The official status is “Reported,” with an investigation confirmed for the cursor customization problem. A public repair date is not stated in the evidence available. 2 Thus, the claim that no formal Known Issue entry exists is outdated or incorrect as of August 30.

• Practical workaround: If the problem affects you, uninstall the preview update: Settings → Windows Update → Update history → Uninstall updates → KB5120998 → Uninstall, then restart. Because KB5120998 is the later optional preview layer, rolling it back should return the PC to the preceding August security-serviced build rather than remove the earlier August security update itself; Microsoft’s August security update for 24H2/25H2 is KB5121003, Build 26100/26200.9168. 4

• September Patch Tuesday: Optional “C” preview-update changes commonly roll into the following monthly cumulative security release—September 8, 2026 in this case—but this is an expectation, not a guarantee that every feature or the cursor defect will ship unchanged or fixed. Microsoft has not published such a commitment or fix timeline. 12

• Quality-assurance interpretation: This is reasonable evidence of a release-validation failure for a widely used personalization path, but it does not establish that QA staffing reductions or AI-driven testing caused it. Microsoft did announce a broader 4,800-role reduction in July while prioritizing AI investments, but the available evidence does not tie those reductions specifically to the Windows QA organization or this defect. 5