Windows 11 KB5074109 now linked to boot failures

[Redaktion]

Microsoft's troubled Windows 11 KB5074109 January 2026 update is now under investigation for causing UNMOUNTABLE_BOOT_VOLUME boot failures on some systems. Affected PCs refuse to start and must be recovered via WinRE, adding a serious new symptom to an already messy Patch Tuesday.

https://www.notebookcheck.net/Windows-11-KB5074109-now-linked-to-boot-failures.1212711.0.html

[tfk, the5krunner]

this update is a disaster causing everyone here multiple problems.
uninstall fixes it but I've spent over a day fixing corrupted pst files for me and some others.