strange. ls: cannot access?
ls -Al /etc/php/7.3/fpm/conf.d/99-dietpi.nextcloud.ini
ls: cannot access ‘/etc/php/7.3/fpm/conf.d/99-dietpi.nextcloud.ini’: No such file or directory
but 
root@DietPi:/etc/php/7.3/fpm/conf.d# ls
10-mysqlnd.ini 20-curl.ini 20-iconv.ini 20-phar.ini 20-sysvmsg.ini 20-zip.ini
10-opcache.ini 20-dom.ini 20-igbinary.ini 20-posix.ini 20-sysvsem.ini 98-dietpi.ini
10-pdo.ini 20-exif.ini 20-intl.ini 20-readline.ini 20-sysvshm.ini 99-dietpi-nextcloud.ini
15-xml.ini 20-fileinfo.ini 20-json.ini 20-redis.ini 20-tokenizer.ini
20-apcu.ini 20-ftp.ini 20-mbstring.ini 20-shmop.ini 20-wddx.ini
20-bcmath.ini 20-gd.ini 20-mysqli.ini 20-simplexml.ini 20-xmlreader.ini
20-calendar.ini 20-gettext.ini 20-pdo_mysql.ini 20-sockets.ini 20-xmlwriter.ini
20-ctype.ini 20-gmp.ini 20-pdo_sqlite.ini 20-sqlite3.ini 20-xsl.ini
A typo, - instead of . 
. Okay so it is enabled.
Can you run and paste the output of: php -i | grep opcache
ooo, typo also here 
php -i | grep opcache
/etc/php/7.3/cli/conf.d/10-opcache.ini,
opcache.blacklist_filename => no value => no value
opcache.consistency_checks => 0 => 0
opcache.dups_fix => Off => Off
opcache.enable => On => On
opcache.enable_cli => Off => Off
opcache.enable_file_override => Off => Off
opcache.error_log => no value => no value
opcache.file_cache => no value => no value
opcache.file_cache_consistency_checks => On => On
opcache.file_cache_only => Off => Off
opcache.file_update_protection => 2 => 2
opcache.force_restart_timeout => 180 => 180
opcache.huge_code_pages => Off => Off
opcache.interned_strings_buffer => 8 => 8
opcache.lockfile_path => /tmp => /tmp
opcache.log_verbosity_level => 1 => 1
opcache.max_accelerated_files => 10000 => 10000
opcache.max_file_size => 0 => 0
opcache.max_wasted_percentage => 5 => 5
opcache.memory_consumption => 128 => 128
opcache.opt_debug_level => 0 => 0
opcache.optimization_level => 0x7FFEBFFF => 0x7FFEBFFF
opcache.preferred_memory_model => no value => no value
opcache.protect_memory => Off => Off
opcache.restrict_api => no value => no value
opcache.revalidate_freq => 1 => 1
opcache.revalidate_path => Off => Off
opcache.save_comments => On => On
opcache.use_cwd => On => On
opcache.validate_permission => Off => Off
opcache.validate_root => Off => Off
opcache.validate_timestamps => On => On
So for CLI all settings are in fact as they should be. Only other idea, does something in Lighttpd override it?
grep -r opcache /etc/lighttpd/
grep -r opcache /etc/lighttpd/
/etc/lighttpd/conf-available/99-dietpi-nextcloud.conf: setenv.add-environment += ( “PHP_ADMIN_VALUE” => “opcache.memory_consumption=128” )
Ah I already had that in mind, we added the memory consumption setting for the Nextcloud subdir only in the past, but that does not work as I thought that time, so we now add it PHP-wide.
Now if why if would cause the warning (as the value still is what it should be) but high change that solves it:
sed -i '/opcache/d' /etc/lighttpd/conf-available/99-dietpi-nextcloud.conf
systemctl restart lighttpd
We won! 
uf, it was a great journey, Tnx!!
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