My setup works as follows:
Laptop via usb-c directly at the display
PC via DP & USB-B

The KVM at the display decides via the display input to which device the USBs are forwarded.

I am not sure if this would work if the laptop did not provide the display output via USB-C. I.e., the dock you are using would have to be able to provide two display outputs via USB-C. Two 4K outputs certainly requires Thunderbolt, but otherwise I can't help with the dock selection.

Funktioniert eventuell diese Kabel vom USB C vom Monitor auf dem Targus USB-C Dual ?
Belkin USB-C TO HDMI 2.1 CABLE 2M (2 m)