Trying to access array offset on value of type bool at /var/www/nextcloud/apps/user_external/lib/base.php#69

Login as admin user into your Nextcloud and access
http://example.com/index.php/settings/integrity/failed
paste the results here.

No errors have been found.

If you have access to your command line run e.g.:
sudo -u www-data php occ app:list
from within your Nextcloud installation folder

Enabled:

• accessibility: 1.6.0
• activity: 2.13.4
• admin_audit: 1.10.0
• apporder: 0.11.0
• breezedark: 20.0.3
• calendar: 2.1.3
• cloud_federation_api: 1.3.0
• comments: 1.10.0
• contacts: 3.4.3
• contactsinteraction: 1.1.0
• dav: 1.16.2
• deck: 1.2.3
• drawio: 0.9.8
• external: 3.7.1
• extract: 1.3.0
• federatedfilesharing: 1.10.2
• federation: 1.10.1
• files: 1.15.0
• files_external: 1.11.1
• files_markdown: 2.3.1
• files_pdfviewer: 2.0.1
• files_rightclick: 0.17.0
• files_sharing: 1.12.2
• files_trashbin: 1.10.1
• files_versions: 1.13.0
• files_videoplayer: 1.9.0
• groupfolders: 8.2.0
• logreader: 2.5.0
• lookup_server_connector: 1.8.0
• nextcloud_announcements: 1.9.0
• notifications: 2.8.0
• oauth2: 1.8.0
• password_policy: 1.10.1
• passwords: 2021.1.2
• photos: 1.2.3
• privacy: 1.4.0
• provisioning_api: 1.10.0
• rainloop: 7.0.3
• recommendations: 0.8.0
• richdocuments: 3.7.11
• serverinfo: 1.10.0
• settings: 1.2.0
• sharebymail: 1.10.0
• support: 1.3.0
• systemtags: 1.10.0
• tasks: 0.13.6
• text: 3.1.0
• theming: 1.11.0
• twofactor_backupcodes: 1.9.0
• updatenotification: 1.10.0
• user_external: 1.0.0
• viewer: 1.4.0
• workflowengine: 2.2.0
  Disabled:
• dashboard
• encryption
• firstrunwizard
• ldap_write_support
• mail
• survey_client
• user_ldap
• user_status
• weather_status

If you have access to your command line run e.g.:
sudo -u www-data php occ config:list system
from within your Nextcloud installation folder

or

Insert your config.php content here.
Make sure to remove all sensitive content such as passwords. (e.g. database password, passwordsalt, secret, smtp password, …)

{
"system": {
"passwordsalt": "REMOVED SENSITIVE VALUE",
"secret": "REMOVED SENSITIVE VALUE",
"trusted_domains": [
"192.168.78.10",
"test.cobios.de",
"0.0.0.0",
"cloud.cobios.de"
],
"trusted_proxies": "REMOVED SENSITIVE VALUE",
"datadirectory": "REMOVED SENSITIVE VALUE",
"dbtype": "mysql",
"version": "20.0.5.2",
"overwrite.cli.url": "https://localhost",
"dbname": "REMOVED SENSITIVE VALUE",
"dbhost": "REMOVED SENSITIVE VALUE",
"dbport": "",
"dbtableprefix": "oc_",
"mysql.utf8mb4": true,
"dbuser": "REMOVED SENSITIVE VALUE",
"dbpassword": "REMOVED SENSITIVE VALUE",
"installed": true,
"instanceid": "REMOVED SENSITIVE VALUE",
"activity_expire_days": 14,
"auth.bruteforce.protection.enabled": true,
"blacklisted_files": [
".htaccess",
"Thumbs.db",
"thumbs.db",
".DS_Store"
],
"cron_log": true,
"enable_previews": true,
"enabledPreviewProviders": [
"OC\Preview\PNG",
"OC\Preview\JPEG",
"OC\Preview\GIF",
"OC\Preview\BMP",
"OC\Preview\XBitmap",
"OC\Preview\Movie",
"OC\Preview\PDF",
"OC\Preview\MP3",
"OC\Preview\TXT",
"OC\Preview\MarkDown"
],
"filesystem_check_changes": 0,
"filelocking.enabled": "true",
"htaccess.RewriteBase": "/",
"integrity.check.disabled": false,
"knowledgebaseenabled": false,
"logfile": "/var/nc_data/nextcloud.log",
"loglevel": 0,
"logtimezone": "Europe/Berlin",
"log_rotate_size": 104857600,
"maintenance": false,
"memcache.local": "\OC\Memcache\APCu",
"memcache.locking": "\OC\Memcache\Redis",
"overwriteprotocol": "https",
"overwritehost": "cloud.cobios.de",
"overwritewebroot": "/",
"overwriteconaddr": "^192.168.78.6$",
"preview_max_x": 1024,
"preview_max_y": 768,
"preview_max_scale_factor": 1,
"redis": {
"host": "REMOVED SENSITIVE VALUE",
"port": 0,
"timeout": 0
},
"quota_include_external_storage": false,
"share_folder": "/Shares",
"skeletondirectory": "",
"theme": "",
"trashbin_retention_obligation": "auto, 7",
"updater.release.channel": "stable",
"user_backends": [
{
"class": "OC_User_SMB",
"arguments": [
"192.168.78.3"
]
}
],
"mail_smtpmode": "smtp",
"mail_smtpsecure": "tls",
"mail_sendmailmode": "smtp",
"mail_from_address": "REMOVED SENSITIVE VALUE",
"mail_domain": "REMOVED SENSITIVE VALUE",
"mail_smtpauthtype": "LOGIN",
"mail_smtpauth": 1,
"mail_smtphost": "REMOVED SENSITIVE VALUE",
"mail_smtpport": "25",
"mail_smtpname": "REMOVED SENSITIVE VALUE",
"mail_smtppassword": "REMOVED SENSITIVE VALUE",
"ldapIgnoreNamingRules": false,
"ldapProviderFactory": "OCA\User_LDAP\LDAPProviderFactory"
}
}

Insert your webserver log here

Nothing special here.

Insert your Nextcloud log here

Too much deprecated class informations and the error described above.

{"reqId":"IfHPJvESYKpMUNArQY3K","level":3,"time":"2021-01-21T15:12:10+01:00","remoteAddr":"192.168.82.32","user":"xxx","app":"PHP","method":"GET","url":"/ocs/v2.php/apps/notifications/a
pi/v2/notifications","message":{"Exception":"Error","Message":"Trying to access array offset on value of type bool at /var/www/nextcloud/apps/user_external/lib/base.php#69","Code":0,"Trace":[
{"file":"/var/www/nextcloud/apps/user_external/lib/base.php","line":69,"function":"onError","class":"OC\Log\ErrorHandler","type":"::"},{"file":"/var/www/nextcloud/lib/private/User/User.php"
,"line":133,"function":"getDisplayName","class":"OCA\user_external\Base","type":"->"},{"file":"/var/www/nextcloud/apps/external/lib/SitesManager.php","line":135,"function":"getDisplayName",
"class":"OC\User\User","type":"->"},{"file":"/var/www/nextcloud/apps/external/lib/AppInfo/Application.php","line":44,"function":"getSitesToDisplay","class":"OCA\External\SitesManager","ty
pe":"->"},{"file":"/var/www/nextcloud/apps/external/appinfo/app.php","line":24,"function":"register","class":"OCA\External\AppInfo\Application","type":"->"},{"file":"/var/www/nextcloud/lib
/private/legacy/OC_App.php","line":289,"args":["/var/www/nextcloud/apps/external/appinfo/app.php"],"function":"require_once"},{"file":"/var/www/nextcloud/lib/private/legacy/OC_App.php","line"
:171,"function":"requireAppFile","class":"OC_App","type":"::"},{"file":"/var/www/nextcloud/lib/private/legacy/OC_App.php","line":131,"function":"loadApp","class":"OC_App","type":"::"},{"file"
:"/var/www/nextcloud/ocs/v1.php","line":56,"function":"loadApps","class":"OC_App","type":"::"},{"file":"/var/www/nextcloud/ocs/v2.php","line":24,"args":["/var/www/nextcloud/ocs/v1.php"],"func
tion":"require_once"}],"File":"/var/www/nextcloud/lib/private/Log/ErrorHandler.php","Line":91,"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (X11; Linux x86_64; rv:84.0) Gecko/20100101 Firefo
x/84.0","version":"20.0.5.2"}

Insert your browser log here, this could for example include:

a) The javascript console log
b) The network log
c) ...