Please take a look at this picture bottom right setup: https://ae01.alicdn.com/kf/H7abd0981989a4e29999b02a73e319726y.png. I just cannot find any KVM product that charge over USB Type C more than one device.
And as I’m really not familiar with but might be very difficult to find something with PD3.0 charging capability in 4-Port KVM setup. But anyway here some “think about” link, as it might happen that this one work with Librem 14 and another one with Type C port, at least as partial (two laptops) solution: https://www.aliexpress.com/item/1005002383464971.html − 2-Ports (2×USB Type C). Especially and if your other laptop have two PD ports, you would charge Librem 14 through its DC port.
If your monitor input is HDMI only: https://www.aliexpress.com/item/1005003202467727.html − 2-Ports (1-Port is USB Type C), not easy wish of yours indeed (as of today), but I don’t know much about current KVM switches anyway.
Please note: Those links are perhaps nothing for real, but at least to give you another “search and buy” idea.