It works for me.
I created the following files,
----------------------------- bar.vim ------------------------------
syn keyword Statement cow
----------------------------- foo.txt ------------------------------
The cow stood in the pasture.
--------------------------------------------------------------------
and ran vim as follows:
$ vim -N -u NONE --cmd 'syntax on' -S bar.vim foo.txt
The word "cow" was highlighted in yellow, as expected.
The vim I used is a normal version, reasonably up to date.
$ vim --version
VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Dec 17 2019 13:33:01)
Included patches: 1-18
Compiled by gary@aurora
Normal version with GTK2 GUI. Features included (+) or not (-):
...
Regards,
Gary