Im having the exact same issue.
100% fresh windows 11 install and all drivers up to date...
When i start KVM in full screen on main monitor and try to press the [1] to change it to second screen it just gets minimized on that screen.
And i cant open it nor interact whit it. And have to end up closing it.
The same issue is if i have the "open sidebar" on the main monitor and press connect it works..
But if i ahve the open sidebar showing on second monitor and press connect it ends up the same just a icon on the taskbar minimized and cant interact whit it other then "close"
But when i minimize the screen and drag it to the second monitor then go full screen it works..
I can also press [2] and move it back to main monitor like it supposed to work.
Best Regards Andreas