PHP Warning: Module "mysqli" is already loaded in Unknown on line 0 Error

Issue

An error during WP installation:

PHP Warning: Module "mysqli" is already loaded in Unknown on line 0 Error: Fout bij het maken van de databaseconnectie.

Environment

• Cloudlinux 8 
• Plesk
• CloudLinux PHP Selector

Solution

Please check the /opt/alt/php81/etc/php.d/default.ini, if there are any mistypes or doubled lines.
For example:

# grep -ri zip.so /opt/alt/php81/etc/php.d/
default.ini:extension=zip.so
default.ini:extension=zip.so
default.ini_bkp:extension=zip.so

And remove them.

Cause

Mistypes in configuration.