The directive disable_functions cannot be changed using the article How to disable PHP functions globally? under Plesk > Tools & Settings > PHP Settings > php_version > php.ini.
After changing the directive disable_functions under Plesk > Domains > example.com > PHP Settings, domain's phpinfo still shows the old value.
The configuration file
/var/www/vhosts/system/example.com/etc/php.inicontains the default value:
# grep "disable_functions" /var/www/vhosts/system/example.com/etc/php.ini
disable_functions = "opcache_get_status"
This is Plesk bug with ID #PPPM-9216, which is planned to be fixed in one of the future product updates.
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In the meanwhile it is possible to use the following workaround: