Maybe this can help a lot for others with Black screen / No mouse or control.
I have 4 laptops and 1 of this laptops has KVM screen without control and a black screen, the others work well. 1 has CPU Intel graphics, 2 has a dedicated NVidia and 1 has CPU AMD graphics. Think graphic adapter has no influence on the KVM.
The difference between this one and the others is the Windows version. (Windows 11 Home instead of Windows 11 Pro)
I thought, only Pro has normally remote desktop and I upgrade the Windows 11 Home to Pro.
After that the first Multiplicity KVM connection give a normal screen and total control.
Conclusion what i think:
Multiplicity KVM / KVM Pro only works on systems with a Windows Pro version.
The only question now, if all KVM Laptops and Computer have Windows 11 Pro why should we need Multiplicity KVM if they all have Windows RDP which looks graphical better and have complete control.