how to create bootable usb stick from iso file

[hlyg <hlyg2023@outlook.com>]

in debian, it is as easy as copying iso file to usb device (/dev/sdx), 
run sync to be safe

does this method work for other iso file?

http://ftp.funet.fi/pub/unix/FreeBSD/releases/ISO-IMAGES/13.1/FreeBSD-13.1-RELEASE-i386-bootonly.iso

i can't boot it created this way. what's wrong with it? Thanks!