Laptop with fresh Manjaro XFCE install. Desktop with nothing installed, plan to install FreeBSD. I have no physical keyboard to interface with the desktop. I do have my laptop with a USB-C port and a cable to USB 3.0, I just don’t know how to create an emulator of sorts that could take input from the laptop keyboard and repeat that information through the USB. Might QEMU be of interest?
Over the network I guess? You could use a KVM switch, or use Barrier which mimics a KVM switch over the network.
Hi and welcome to the Forum 
To be able to install anything on your Desktop, you are required to have a keyboard.
Because the BIOS will only accept input from it’s own direct hardware.
Even changing BIOS settings need this, fe to setup PXE 
After having installed and configured an Operating System you might be able to use different utilities to receive input from other sources, but not before it.