CI 4 not working

look in xampp\php\php.ini

try change ;extension=intl to extension=intl

in theory with xampp you are probably using some form of Linux ? since from memory windows is wamp or similar.
There are a few options for developing CI4 if you have Linux .

Simply use apache on Linux , better than xampp

Just put Dev directory on desktop and use spark serve to fire up dev http services; use sqlite for database

use free live web hosting such as 000webhost