site crash with PHP8

Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /home/public_html/wp-includes/class-wpdb.php:1807 Stack trace: #0 /home/public_html/wp-includes/class-wpdb.php(734): wpdb->db_connect() #1 /home/public_html/wp-includes/load.php(562): wpdb->__construct() #2 /home/public_html/wp-settings.php(124): require_wp_db() #3 /home/public_html/wp-config.php(205): require_once(‘/home/…’) #4 /home/public_html/wp-load.php(50): require_once(‘/home/…’) #5 /home/public_html/wp-admin/admin.php(34): require_once(‘/home/…’) #6 /home/public_html/wp-admin/plugins.php(10): require_once(‘/home/…’) #7 {main} thrown in /home/public_html/wp-includes/class-wpdb.php on line 1807

There has been a critical error on this website.

Switching from 7.4 to 8.0 produces the above error. Switched to 2023 and renamed the plugin folder, but that didn’t help. Saw another post about making sure that “mysqli” is running, but I checked and that is, so not sure what else is triggering this.

This is my second or third site in multisite mode that I can’t upgrade to PHP8, so its starting to seem like a pattern.