What version of PHP are you trying to run?
8.1 ive been told not to go any higher yet.
What version of ZenCart?
v2.0.1
It turned out to be a coding issue where the dev 'assumed' various paths and didn't actually check them.
Its an option in the settings. Ive put it it to
/var/lib/php/sw-zen/session
But that location is empty. Looking at the phpinfo i notice this
session.save_handler user files
which to me is saving them as 'user' whatever that means and might explain why the folder is empty
Thanks re the samesite cookie setting. Ill hold of on that for now till I find the sessions file location