pg_connect: Call to undefined function pg_connect()

I have moved a number of php scripts from PHP 7.2.9 to PHP 8.0.27 and I am encountering the following error: [05-Dec-2023 15:34:41 America/Toronto] PHP Fatal error: Uncaught Error: Call to undefined function pg_connect() in /usr/httpd/xxx0002.php:211 line 211, which worked as expected up until now is: $db_handle = pg_connect('dbname=xxxx user=xxxx password=xxxx'); and the online docs show this as still acceptable but deprecated. I noticed that the result will be a "PgSql\Connection" object. Two questions: 1. since the syntax is still valid why am I getting an undefined function error? 2. since the result is different, am I going to encounter a lot of other problems in this conversion and where can I find a full list of these changes? Thanks, John ======