After doing a apt upgrade i had the problem with getting a internal server error and my log in nginx nextcloud.error.log said this:
FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught Error: Class ‘OCA\DAV\Connector\Sabre\ExceptionLoggerPlugin’ not found in /var/www/nextcloud/remote.php
I solved the problem with:
apt install php7.3-zip php7.3-gd php7.3-redis php7.3-memcached php7.3-apcu
just for future reference