While Build 21390 did not introduce sweeping system overhauls—as Microsoft was reserving major announcements for its official next-generation unveiling—it did bring several notable quality-of-life improvements:
Exploring Windows 10 Insider Preview Build 21390 (x86/x64 ISO Incl)
According to Microsoft’s official release notes, several bugs were addressed:
Before installing Build 21390, consider the following:
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Build 21390 resolved several annoying bugs and stability issues:
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Given that Microsoft no longer offers Build 21390 officially, users must rely on third-party sources. The most reliable and widely recommended method is , a community-driven project that generates ISO files directly from Microsoft's Unified Update Platform (UUP) files.
: Clean installations of this build removed the Mail and Microsoft Store apps from the default pinned taskbar set. Performance & Stability While Build 21390 did not introduce sweeping system
Occasional crashes when opening File Explorer were noted in this series of builds. How to Get Windows 10 Insider Preview Build 21390 ISO
Windows 10 Insider Preview (codename "Cobalt") was a minor but visually significant update released to the Dev Channel in May 2021. While it lacked major feature overhauls, it served as a late-stage bridge toward what would eventually become Windows 11, introducing several "Sun Valley" visual elements. Key Features & Visual Improvements
. It is notable as the final Insider Preview build before the transition to Windows 11 development, and it was the last build to feature the classic Windows 10 user interface while incorporating early Windows 11 elements like updated icons. Key Features and Improvements Updated Iconography : New Fluent-inspired icons for the Task Manager MSI installers Default Terminal : Added the ability to set Windows Terminal Preview (version 1.9 or higher) as the default terminal emulator. Performance and Stability
| Architecture | Availability | Unique Significance | |--------------|--------------|----------------------| | | Available via UUPDump and third-party archives | The last Windows 10 build to support 32-bit processors | | x64 (64-bit) | Widely available | Standard modern hardware support | | ARM64 | Available (last ARM64 Dev build) | Final Windows 10 ARM64 build before Windows 11; key for Raspberry Pi and Apple M-series compatibility | The most reliable and widely recommended method is
Microsoft used Build 21390 as a testbed for its "servicing pipeline" — the system that delivers updates — by releasing multiple cumulative updates on top of the same base build. Here's the full timeline:
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Developers utilizing WSL benefit from structural updates in this build.