can’t work with unix socket

It seems that NF doesn’t work with unix socket to access the DB on local mysql server.
ie. In file wp-config.php I just set:
define( 'DB_HOST', '/var/run/mysqld/mysqld.sock' );
instead of:
define( 'DB_HOST', 'localhost' );

whilst WP works as before, NF shows this error in admin page:
NinjaFirewall fatal error: Cannot connect to WordPress database. Review your installation, your site is not protected.

I have seen other threads where you recommend to create a file wp-db.php so I did, this is the output:

Version: 1.9
Found /var/www/html/mysite.org/wp-config.php.
Opening it for reading.
Looking for DB_NAME, DB_USER, DB_PASSWORD, DB_HOST and $table_prefix:

    DB_NAME: found 'WP'
    DB_USER: found 'WordPressUser'
    DB_PASSWORD: found (click here to view password)
    DB_HOST: found '/var/run/mysqld/mysqld.sock'
    table_prefix: found 'wp_'

Attempting to connect to the DB:
Warning: mysqli::real_connect(): php_network_getaddresses: getaddrinfo failed: Name or service not known in /var/www/html/mysite.org/wp-db.php on line 100

Warning: mysqli::real_connect(): (HY000/2002): php_network_getaddresses: getaddrinfo failed: Name or service not known in /var/www/html/mysite.org/wp-db.php on line 100
Connection Error: php_network_getaddresses: getaddrinfo failed: Name or service not known

Exiting.

I have also run the wp-check.php script, this is the output:

NinjaFirewall (WP edition) troubleshooter
HTTP server 	: 	nginx/1.18.0
PHP version 	: 	7.4.3
PHP SAPI 	: 	FPM-FCGI
 	 	 
auto_prepend_file 	: 	none
wp-config.php 	: 	found in /var/www/html/mysite.org/wp-config.php
NinjaFirewall detection 	: 	NinjaFirewall WP Edition is loaded (WordPress WAF mode)
 	 	 
Loaded INI file 	: 	/etc/php/7.4/fpm/php.ini
user_ini.filename 	: 	.user.ini
user_ini.cache_ttl 	: 	300 seconds
User PHP INI 	: 	.user.ini found -
 	 	 
DOCUMENT_ROOT 	: 	/var/www/html/mysite.org
ABSPATH 	: 	/var/www/html/mysite.org/
WordPress version 	: 	5.7.2
WP_CONTENT_DIR 	: 	/var/www/html/mysite.org/wp-content
Plugins directory 	: 	/var/www/html/mysite.org/wp-content/plugins
User Role 	: 	Administrator
User Capabilities 	: 	manage_options: OK - unfiltered_html: OK
Log dir permissions 	: 	/var/www/html/mysite.org/wp-content/nfwlog dir is writable
Cache dir permissions 	: 	/var/www/html/mysite.org/wp-content/nfwlog/cache dir is writable

NinjaFirewall (WP edition) troubleshooter v1.9.4

thanks for any help!