Still Error 504 Gateway Timeout

Nextcloud version (20.0.7): Via Nextcloudpi Image
Operating system and version Nextcloudpi Image: Raspberry, I think it’s Debian
Apache or nginx version: I use Nginx as a Reverse Proxy
PHP version (7.3)

I get the following error message in the WEB UI: Error when assembling chunks, status code 504. And in the Windows client I get a similar message: “504 Gateway Timeout”.
Moreover, I use this for the Nginx reverse proxy. I have set up the Nextlcoud with the Nextcloudpi image from ownyourbits.com.
The tips from this post did not help me.
But this only happens with larger files.
How can I fix the problem?

Is this the first time you’ve seen this error? (Y/N): YES

The output of your Nextcloud log in Admin > Logging:

The output of your config.php file in /var/www/nextcloud:

<?php $CONFIG = array ( 'passwordsalt' => 'uUUku6VUbelrV2ZVnRWwfZYLvPE19q', 'secret' => 'FA/fhDyPkDShfWoOIlCye+0m8mgva+C3mH5ceaGzBIA3sowU', 'trusted_domains' => array ( 0 => 'localhost', 5 => 'nextcloudpi.local', 7 => 'nextcloudpi', 8 => 'nextcloudpi.lan', 11 => '2a02:810d:47bf:defc:ff6:42******, 1 => '192.168.178.**', 20 => '*******.org', 12 => '*******.org', ), 'datadirectory' => '/media/myCloudDrive/ncdata', 'dbtype' => 'mysql', 'version' => '20.0.7.1', 'overwrite.cli.url' => 'https://*******.org/', 'dbname' => 'nextcloud', 'dbhost' => 'localhost', 'dbport' => '', 'dbtableprefix' => 'oc_', 'mysql.utf8mb4' => true, 'dbuser' => 'ncadmin', 'dbpassword' => 'w252B8Q+GDcUR+NrcpadB*********, 'installed' => true, 'instanceid' => 'ocwn0g3teaag', 'memcache.local' => '\\OC\\Memcache\\Redis', 'memcache.locking' => '\\OC\\Memcache\\Redis', 'redis' => array ( 'host' => '/var/run/redis/redis.sock', 'port' => 0, 'timeout' => 0.0, 'password' => 'OivzKMvko7PbVw7lwUzBAjqQv1If6Ddm/9******, ), 'tempdirectory' => '/media/myCloudDrive/ncdata/tmp', 'mail_smtpmode' => 'sendmail', 'mail_smtpauthtype' => 'LOGIN', 'mail_from_address' => 'admin', 'mail_domain' => 'ownyourbits.com', 'preview_max_x' => '2048', 'preview_max_y' => '2048', 'jpeg_quality' => '60', 'overwriteprotocol' => 'https', 'maintenance' => false, 'logfile' => '/media/myCloudDrive/ncdata/nextcloud.log', 'dbuser' => 'ncadmin', 'dbpassword' => 'w252B8Q+GDcUR+NrcpadB/jTs7GilsNzqp8C0IG6VGg=', 'installed' => true, 'instanceid' => 'ocwn0g3teaag', 'memcache.local' => '\\OC\\Memcache\\Redis', 'memcache.locking' => '\\OC\\Memcache\\Redis', 'redis' => array ( 'host' => '/var/run/redis/redis.sock', 'port' => 0, 'timeout' => 0.0, 'password' => 'OivzKMvko7PbVw7lwUzBAjqQv1If6Ddm******, ), 'tempdirectory' => '/media/myCloudDrive/ncdata/tmp', 'mail_smtpmode' => 'sendmail', 'mail_smtpauthtype' => 'LOGIN', 'mail_from_address' => 'admin', 'mail_domain' => 'ownyourbits.com', 'preview_max_x' => '2048', 'preview_max_y' => '2048', 'jpeg_quality' => '60', 'overwriteprotocol' => 'https', 'maintenance' => false, 'logfile' => '/media/myCloudDrive/ncdata/nextcloud.log', 'loglevel' => '2', 'log_type' => 'file', 'updater.secret' => '$2y$10$oR1/mZRi6BlkyifvmREv9uNLZH.WS2WG0Wi1fxjen/KTreVB4Jrh2', 'theme' => '', ); The output of your Apache/nginx/system log in `/var/log/____`: Where can I find this at Nextcloudpi?