Internal Server Error after Upgrade to Deb10

Hey,

I use a Nextcloud 15.0.10 installation hosted on my own Debian Server.

With apt-get update, apt-get upgrade and apt-get upgrade I upgraded from Debian 9 to 10. Worked fine!

All my sites are reachable as usual. Only expectation is my nextcloud homepage.
I get the following message shown:

"Internal Server Error

The server encountered an internal error and was unable to complete your request.
Please contact the server administrator if this error reappears multiple times, please include   the technical details below in your report.
More details can be found in the server log."

The nextcloud.log says the following:

{"reqId":"yLCKjvMxDLMGV5eSGJUO","level":3,"time":"2019-07-   28T15:27:49+00:00","remoteAddr":"91.106.187.199","user":"--","app":"remote","method":"GET","url":"\/nextcloud\/sta$
{"reqId":"5jPebuCSPiTy95oaiWyq","level":3,"time":"2019-07-28T15:27:51+00:00","remoteAddr":"91.106.187.199","user":"--","app":"PHP","method":"GET","url":"\/nextcloud\/ocs\/v$
{"reqId":"t28j09H5e3CpmD1O0llx","level":3,"time":"2019-07-28T15:28:21+00:00","remoteAddr":"91.106.187.199","user":"--","app":"remote","method":"GET","url":"\/nextcloud\/sta$
{"reqId":"xuFLolL1wfWlCVglYH81","level":3,"time":"2019-07-28T15:28:23+00:00","remoteAddr":"91.106.187.199","user":"--","app":"PHP","method":"GET","url":"\/nextcloud\/ocs\/v$
{"reqId":"IsBOy3YM9rAjWqjCTRIR","level":3,"time":"2019-07-28T15:28:51+00:00","remoteAddr":"91.106.187.199","user":"--","app":"remote","method":"OPTIONS","url":"\/nextcloud\$
{"reqId":"IsBOy3YM9rAjWqjCTRIR","level":3,"time":"2019-07-28T15:28:51+00:00","remoteAddr":"91.106.187.199","user":"--","app":"core","method":"OPTIONS","url":"\/nextcloud\/r$
{"reqId":"IsBOy3YM9rAjWqjCTRIR","level":3,"time":"2019-07-28T15:28:51+00:00","remoteAddr":"91.106.187.199","user":"--","app":"core","method":"OPTIONS","url":"\/nextcloud\/r$
{"reqId":"kPdagQxtlppZ6pbNJ8Vp","level":3,"time":"2019-07-28T15:28:53+00:00","remoteAddr":"91.106.187.199","user":"--","app":"remote","method":"GET","url":"\/nextcloud\/sta$
{"reqId":"xG0EiSlbx3kEaq0CfQJT","level":3,"time":"2019-07-28T15:28:55+00:00","remoteAddr":"91.106.187.199","user":"--","app":"PHP","method":"GET","url":"\/nextcloud\/ocs\/v$

The only thing I did, after the Upgrade to Deb10, is installing the php-mysql package, as it was not available anymore after the upgrade.

Finally, my config.php:

<?php
$CONFIG = array (
  'instanceid' => '***',
  'passwordsalt' => '***',
  'secret' => '***',
  'trusted_domains' => 
  array (
0 => '192.168.178.32',
1 => '***.org',
  ),
  'datadirectory' => '/Nextcloud',
  'htaccess.RewriteBase' => '/nextcloud',
  'overwrite.cli.url' => 'https://***.org/nextcloud',
  'dbtype' => 'mysql',
  'version' => '15.0.10.0',
  'dbname' => '***',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => '***',
  'dbpassword' => '***',
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'memcache.locking' => '\\OC\\Memcache\\Redis',
  'filelocking.enabled' => 'true',
  'redis' => 
  array (
    'host' => 'localhost',
    'port' => 6379,
    'timeout' => 0.0,
  ),
  'installed' => true,
  'maintenance' => false,
  'loglevel' => 2,
  'logfile' => '/var/log/nextcloud/nextcloud.log',
  'mail_smtpmode' => 'smtp',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpauth' => 1,
  'mail_smtpsecure' => 'tls',
  'mail_from_address' => '***',
  'mail_domain' => 'web.de',
  'mail_smtphost' => 'smtp.web.de',
  'mail_smtpport' => '587',
  'mail_smtpname' => '***',
  'mail_smtppassword' => '***',
  'theme' => '',
  'updater.secret' => '***',
  'mysql.utf8mb4' => true,
  'updater.release.channel' => 'stable',
);

I did not change anything in the config after the upgrade to Deb10.

Can someone please help me? I have no idea…