Well, you really need to help us more by giving infos about your settings, like what system you are on, what is your actual locale setting in php.ini, lang.english.php or whatever language file you use?
Did you add some code to set timezone in Zen Cart?...
With information I have now, here is what I can see:

Your problem is not related to this thread original post that was a bug in a specific PHP version you do not used.
The problem disappears when using PHP 8.0 or lower because in these cases Zen Cart do not use IntlDateFormatter.
IntlDateFormatter crashes PHP because it is given bad information/settings.
Probably not the solution but in php.ini, you should have
PHP Code:
date.timezone = "Europe/Athens" 
rather than
PHP Code:
date.timezone = Europe/Athens 
.

When timezone or other necessary setting is not define in the code, IntlDateFormatter uses PHP's one (good or bad) and if PHP's locale/timezone is not set, PHP will try to use system setting with more or less success depending on system.