Nextcloud version (eg, 20.0.5): 20something (cannot log in, so I can't check)
Operating system and version (eg, Ubuntu 20.04): Ubuntu 18.04 LTS 64bit
Apache or nginx version (eg, Apache 2.4.25): don't know
PHP version (eg, 7.4): 7.3.29
The issue you are facing:
After (without success) trying to add external storage (tried SFTP and WebDav), I now cannot login in via the web interface, synchronisation icon on my Windows client is also grey. 
Error message on the web:
Storage with mount id 2 is not available
Storage is temporarily not available
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
The output of your Nextcloud log in Admin > Logging:
- cannot log in, so no access
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'instanceid' => '***',
'passwordsalt' => '***',
'secret' => '***',
'trusted_domains' =>
array (
0 => 'cloud.integrale-akademie.online',
),
'datadirectory' => '/var/www/vhosts/integrale-akademie.online/cloud.integrale-akademie.online/data',
'dbtype' => 'mysql',
'version' => '20.0.4.0',
'overwrite.cli.url' => 'https://cloud.integrale-akademie.online',
'dbname' => '***',
'dbhost' => 'localhost:3306',
'dbport' => '',
'dbtableprefix' => 'oc_',
'mysql.utf8mb4' => true,
'dbuser' => '****',
'dbpassword' => '****',
'installed' => true,
'loglevel' => 3,
'memcache.local' => '\\OC\\Memcache\\APCu',
'app_install_overwrite' =>
array (
0 => 'groupfolders',
),
'quota_include_external_storage' => false,
'trashbin_retention_obligation' => 'auto, 7',
'login_form_autocomplete' => false,
'knowledgebaseenabled' => false,
'log_rotate_size' => 10485760,
'force_language' => 'de',
'force_locale' => 'de_DE',
'auth.bruteforce.protection.enabled' => true,
'blacklisted_files' =>
array (
0 => '.htaccess',
1 => 'Thumbs.db',
2 => 'thumbs.db',
),
'cron_log' => true,
'maintenance' => false,
'theme' => '',
'twofactor_enforced' => 'true',
'twofactor_enforced_groups' =>
array (
),
'twofactor_enforced_excluded_groups' =>
array (
),
);
The output of your Apache/nginx/system log in /var/log/____:
cannot find that file 🤷♂️
