In "Nextcloud 13 Administration Manual" are written under "Enable PHP OPcache" (1) some values.
These values will be checked in nc under admin -> settings -> Default settings.
If any value is not the same like these guide an error will be shown.
Please only check if opchache is enabled and the values are in range to the values in documentation.
these error message will be confusing users with no completely technical background.
(1)
https://docs.nextcloud.com/server/13/admin_manual/configuration_server/server_tuning.html?highlight=opcache#enable-php-opcache