Windows 11 KB5124010 Brings Back File Explorer Previews for Downloaded Files

Have you also been frustrated by File Explorer’s preview pane since October 2025? With the optional KB5124010 update, Microsoft is easing the preview rules for files coming from the web. Here’s what you need to know about this September 2026 preview update.

On September 22, 2026, Microsoft released the KB5124010 update for Windows 11 24H2 and 25H2, bringing both versions to builds 26100.9550 and 26200.9550. This is an optional update designed to let users test the new features and fixes included in the mandatory update scheduled for October 2026. As a reminder, this type of update does not include security fixes.

This KB has one notable characteristic, as it marks the end of the road for certain Windows 11 24H2 editions. "The September 2026 non-security preview update, KB5124010, is the last update of this type for Windows 11, version 24H2", Microsoft states. In fact, for Windows 11 24H2 Home and Pro editions, the last mandatory update will be released on October 13, 2026, so this is the final one of its kind. Enterprise and Education editions are supported until October 12, 2027.

With that clarified, let’s take a look at KB5124010.

File Explorer: PDF previews are back

As a reminder, since the October 14, 2025 security updates, File Explorer has refused to preview files marked with the Mark of the Web, meaning files downloaded from the Internet. At the time, users panicked, and I had even published an article about this File Explorer preview pane becoming unusable with KB5066835. Microsoft later confirmed that this was an intentional choice. According to the Redmond company, the goal was to block an NTLM hash leak when previewing files containing HTML tags pointing to external paths. So this was a security measure.

One year later, Microsoft is changing course. With KB5124010, the behavior changes because a new button lets users force preview for HTML files, while still respecting the Windows warning. Microsoft also explains that non-HTML files, such as PDFs, are now previewed automatically. Blocking remains in place for HTML files, while other formats get more flexibility. As a result, there is no longer any need to unblock each file individually in its properties. A relief for users, though let’s hope there is no negative security impact.

File Explorer also benefits from other tweaks:

• Home: the Home page now remembers the state of sections (expanded or collapsed), so you can pick up where you left off.
• Details pane: thumbnails for files stored in the cloud are displayed more reliably, and the pane has been reorganized to make file properties easier to read.
• Address bar: Microsoft fixed a bug that could clear its contents when you clicked near the right edge to enter edit mode.

Copilot key, emojis, accessibility: the other new features

The list of new features goes beyond Windows File Explorer. Here are the most interesting ones:

• Copilot key: a new setting lets you remap it so it works like the right Ctrl key or the Menu key.
• Open magnified apps: this new accessibility setting, available under Settings > Accessibility > Visual effects, automatically opens app windows in full screen. It is especially useful for screen reader and Magnifier users, who also get a modernized toolbar.
• Emoji 17.0: Windows 11 now supports this new emoji set (with a furry creature among the emojis—hopefully that makes you happy to be on Windows).
• Tips widget: this new widget delivers short tips about Windows features. It can be added to the widgets board or the lock screen via Settings > Personalization > Lock screen.
• Touchpad: two gestures are now available under Settings > Bluetooth & devices > Touchpad: one-finger vertical scrolling from the left or right edge, and automatic scrolling when your fingers approach the edge.
• Photo backup: a new option lets you back up photos from your smartphone to OneDrive, with setup completed on the phone using a QR code.
• Settings: the Installed apps page now finally shows the version number of packaged apps.
• Desktop background: DIB format is now supported, and slideshow mode now works across multiple virtual desktops.
• Bluetooth: several fixes improve reliability, including a crash (error code 0x139) during audio streaming, as well as support for LE Audio accessories.

On the admin side, there are a few small additions that may be of interest. First, Microsoft mentions—without going into much detail—a remote management plug-in for WinRE that allows MDM vendors to extend their recovery environment administration capabilities. Next, kiosk mode configuration is changing: the Windows + Tab shortcut is disabled in kiosk mode with the restricted experience, while Windows + A and Windows + C are disabled in single-app kiosk mode. Finally, the PC-to-PC migration feature, which let users transfer files and settings directly from the old computer, is no longer available. Microsoft is now steering users toward the Windows Backup tool.

File History fixed, two bugs still remain

On the fixes side, KB5124010 resolves a problem that had been making headlines: File History could fail to back up or restore files on an external drive or network location, with a misleading “Reconnect your drive” message. Earlier this week, I also published an article on the topic: September 2026 updates break File History. So that issue is now fixed, at least with this optional update.

The update also fixes three bugs in Sysmon, as well as an issue with the built-in camera that could stop working.

However, two known issues are still present.

The first affects devices joined to an Active Directory domain, which may lose their trust relationship after installing KB5124008 because of the Machine Identity Isolation feature. In another article, I detailed Microsoft’s workaround for this trust relationship bug. Microsoft says a future update will temporarily prevent this feature from being applied, but that is not yet the case with KB5124010. The second issue affects some USB Audio Class 1.0 devices, which may show Error Code 10 or stop producing sound altogether. No fix is available at this time.

You can find full details about this update on the Microsoft website.

Florian Burnel Co-founder of IT-Connect

Systems and network engineer, co-founder of IT-Connect and Microsoft MVP "Cloud and Datacenter Management". I'd like to share my experience and discoveries through my articles. I'm a generalist with a particular interest in Microsoft solutions and scripting. Enjoy your reading.

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