No monitors detected after macOS Tahoe 26.3.1 update - DisplayLink Manager 15.1

[automised_matt]

DisplayLink Manager 15.1 fails to detect any monitors on macOS Tahoe 26.3.1. The dock is fully functional at the USB level (peripherals work, device appears in system_profiler USB tree) but no virtual framebuffers are created.

Setup:
- macOS 26.3.1 (25D771280a)
- MacBook Pro 16" M1 Pro
- DisplayLink Manager 15.1
- Dell D6000 (DL-6950)
- FileVault enabled
- Monitors worked immediately prior to the 26.3.1 update

Diagnostics:
- system_profiler SPDisplaysDataType shows built-in display only
- ioreg confirms DisplayLinkUserAgent has claimed USB interfaces
- TCC logs confirm Screen Recording permission is granted (authValue=1)
- BetterDisplay also does not detect external displays
- Full uninstall/reinstall, tccutil reset, plist deletion, dock power cycles - none resolve it

Root cause appears to be this error in the DisplayLinkUserAgent process log:

Couldn't read values in CFPrefsPlistSource (Domain: 73YQY62QM3.com.displaylink.DisplayLinkShared, User: kCFPreferencesAnyUser, ByHost: Yes, Container: (null), Contents Need Refresh: Yes): Using kCFPreferencesAnyUser with a container is only allowed for System Containers, detaching from cfprefsd

The shared preferences domain 73YQY62QM3.com.displaylink.DisplayLinkShared does not exist on disk. It looks like Tahoe 26.3 tightened enforcement of container rules for kCFPreferencesAnyUser, preventing DL Manager from reading or creating its shared preferences.

Anyone else seeing this on 26.3? Have filed a support ticket as well.