Everyone can test by -s 30,xhci,passthru.vid.pid,passthru.vid.pid where vid and pid are hex value of vendor id and product id. Only one same device can be passthrough at the same time. Can pass through at most 8 devices.
Or using https://github.com/freebsd/vm-bhyve/pull/36.
Have tested by FreeBSD14, FreeBSD15, Linux Kernel 5.14.8:
A USB 1.0 kbd.
A USB 2.0 kbd.
A USB 2.0 kbd + mouse + touchpad.
A USB 3.0 mass storage.