Not really… If you are in a situation where you have to worry about your USB keyboard pretending to be a NIC to snoop on your traffic, having the schematic doesn’t really help (unless you dis/assemble it yourself). The typical threat vector is external USB drives and the like. They often have terribly insecure firmware, so an attacker can reflash the firmware with one that will pretend to be a keyboard and network card, and these days an external monitor, and then use the keyboard to launch an automated attack on the system.
And no, using only CC USB drives doesn’t really help either, if the firmware can be updated on the drive. In part because someone could still upload a nefarious payload to the drive if you plug it into another machine, and in part because having a trusted USB drive does not prevent the “evil maid” from plugging in an untrusted USB drive.