How to display only specific Error types in debug.log? No notices, warnings, etc

I can’t find the right way to make it work.
I tried many things, like putting this in wp-config.php

define('WP_DEBUG', true);
define('WP_DEBUG_DISPLAY', false);
define('WP_DEBUG_LOG', 'wp-content/themes/mytheme/mylog.log' ); // yeah, customized it a bit. It logs everything
ini_set('error_reporting', E_ERROR );

also tried to set it in the php.ini on various websites i manage.
Not on managed hosting. Or at least not on the well known international ones.
Can it be server side or syntax error, or not even possible what i want?

Thanks!