VNC Server 6.9.0 has been released to automatically use polling when this bug is detected.
We are aware of some customers experiencing a flashing black screen when connecting to VNC Server running on Windows 11.
Our development team have identified this issue as being caused by a bug in DirectX capture in Windows 11 itself, when using at least 1 monitor in a portrait orientation, which will need to be fixed by Microsoft. In the meantime, we are working on an updated version of VNC Server that will automatically fall back to polling when the error caused by the DirectX bug is detected.
Until the updated version of VNC Server is available, if you are affected by this you can resolve the issue by disabling DirectX tracking in VNC Server's Options, Troubleshooting section.
This can also be configured by changing the CaptureMethod parameter in the Expert section to a value of 1.