Ah, when I did try to make my YubiKey work, I added a bunch of configuration, which hw.usb.usbhid.enable=0 was in /boot/loader.conf. I removed it, and it looks like it now defaults to 1. Probably new to 15.0.
It feels good to have the FN key working under GhostBSD finally. For years, I have tried to figure it out. All that time, only one line was needed in sysctl.conf: hw.usb.usbhid.enable=1.
That said, why can FreeBSD have that on by default or automatically?