You can connect peripherals such as keyboard, mouse and monitors to the HP Thunderbolt Dock 120W G4 and use both PCs with it, but there are some limitations and considerations you should be aware of:

## Compatibility
- The HP Thunderbolt Dock 120W G4 is compatible with MacBooks, including the MacBook Pro M4, as well as Windows and Chrome OS systems.

## Connections
- The dock offers various ports such as USB-A 3.0, USB-C, HDMI, DisplayPort and RJ45, which makes it possible to connect multiple peripherals.

## Use with both PCs
- You can connect the keyboard and mouse via the USB ports on the dock and then use them via the dock with your MacBook Pro and your desktop PC.
- For the monitor that you want to connect directly to your desktop PC, you can set the input source on the monitor separately, as you have already planned.
- However, to use both PCs with the same peripherals, you would have to switch between the two devices, as the dock does not support two host devices at the same time. You could therefore connect the dock to either your MacBook Pro or your desktop PC and then use the peripherals via the dock.

## Switching between the devices
- There is no way to configure the dock so that it is connected to both PCs at the same time. So you have to switch the dock manually between the two devices if you want to use the peripherals with the other PC.

Overall, the HP Thunderbolt Dock 120W G4 is a good solution for managing your peripherals, but it requires manual switching between the two PCs.