Option 1:
You can modify the "Welcome to FreeBSD" message in the boot menu frame in
/boot/lua/drawer.lua, line 202, to print for example "Welcome to FreeBSD 12.1-RELEASE-p2".
Option 2:
You can display the version above the boot menu, in the "brand" section, for that modify in
/boot/lua/drawer.lua the
freebsd_brand section, line 280. To determine the position of the message above the boot menu you need to add empty lines and spaces.
Option 3:
You can create a custom logo next to the boot menu. Copy one of the
/boot/lua/logo-*.lua files as draft, rename it, ex
logo-custom.lua, modify text (here also you need to add empty lines and spaces to determine the position of the message),
[EDIT: Change line
drawer.addLogo("...."), { to
drawer.addLogo("custom"), { ], add
loader_logo="custom" in
/boot/loader.conf.
All of the solution are static, I don't see any possibility to print the version dynamically, as it is when you log in, the file system is not mounted yet, no executable like
uname(1) or
freebsd-version(1) available. At any version update the configuration must be updated accordingly .
