ventoy_geom kernel mod is used to boot FreeBSD and other Unix distros.
This kernel mod need to build inside a FreeBSD system.

use VM to install a FreeBSD (e.g.  9.X/10.X/11.X/....), need to install source code.
copy these files for example:  Unix/ventoy_unix_src/FreeBSD/geom_ventoy_src/10.x/sys to /sys directory.
cd /sys/modules/geom/geom_ventoy/
make
make install

Other distros are similar.