The PHP OPcache module in VM

The PHP OPcache module is not properly configured. The OPcache interned strings buffer is nearly full. To assure that repeating strings can be effectively cached, it is recommended to apply “opcache.interned_strings_buffer” to your PHP configuration with a value higher than “24”.

Any idea how to fix this alert? is this not a part of installation script?

Nextcloud is usually installed on a system with a pre-configured web server with PHP enabled. The admin needs to take care of a correct PHP configuration. Detailed information can be found in the admin guide.