Microsoft confirms the error in the new Insider Preview:
Announcing Windows 11 Insider Preview Build 26120.4230 (Beta Channel) (June 2, 2025)
[Graphics]
- *[NEW]*When connecting your PC to some older Dolby Vision displays, in some cases you might see severe discoloration. You can navigate to Settings > System > Display > HDR turn off “Use Dolby Vision mode” as a workaround to resolve the issue or disconnect the display.
Announcing Windows 11 Insider Preview Build 26120.4230 (Beta Channel) | Windows Insider Blog