I do something similar to the post's two-cable configuration:
- Mac to Caldigit TB dock to two displays. - PC to one of the displays - Keyboard and mouse to a USB switch, which connects to the PC and the TB dock
It's kind of a pain to manually flip both the USB switch and the monitor's input.
This app can theoretically help by programmatically toggling the display's input when particular USB devices are dis/connected:
https://github.com/haimgel/display-switch
.. but compatibility is spotty, relying on a rarely-used hardware feature in the display that seems to not be reliably implemented ("DDC/CI").