Got this error with a fresh install of nextcloud in a truenas server.
PHP does not seem to be setup properly to query system environment variables. The test with getenv(“PATH”) only returns an empty response. Please check the installation documentation 
for PHP configuration notes and the PHP configuration of your server, especially when using php-fpm.
Some app directories are owned by a different user than the web server one. This may be the case if apps have been installed manually. Check the permissions of the following app directories:
/usr/local/www/nextcloud/apps-pkg/accessibility
/usr/local/www/nextcloud/apps-pkg/activity
/usr/local/www/nextcloud/apps-pkg/admin_audit
/usr/local/www/nextcloud/apps-pkg/cloud_federation_api
/usr/local/www/nextcloud/apps-pkg/comments
/usr/local/www/nextcloud/apps-pkg/contactsinteraction
/usr/local/www/nextcloud/apps-pkg/dashboard
/usr/local/www/nextcloud/apps-pkg/dav
/usr/local/www/nextcloud/apps-pkg/encryption
/usr/local/www/nextcloud/apps-pkg/federatedfilesharing
/usr/local/www/nextcloud/apps-pkg/federation
/usr/local/www/nextcloud/apps-pkg/files
/usr/local/www/nextcloud/apps-pkg/files_external
/usr/local/www/nextcloud/apps-pkg/files_pdfviewer
/usr/local/www/nextcloud/apps-pkg/files_rightclick
/usr/local/www/nextcloud/apps-pkg/files_sharing
/usr/local/www/nextcloud/apps-pkg/files_trashbin
/usr/local/www/nextcloud/apps-pkg/files_versions
/usr/local/www/nextcloud/apps-pkg/files_videoplayer
/usr/local/www/nextcloud/apps-pkg/firstrunwizard
/usr/local/www/nextcloud/apps-pkg/logreader
/usr/local/www/nextcloud/apps-pkg/lookup_server_connector
/usr/local/www/nextcloud/apps-pkg/nextcloud_announcements
/usr/local/www/nextcloud/apps-pkg/notifications
/usr/local/www/nextcloud/apps-pkg/oauth2
/usr/local/www/nextcloud/apps-pkg/password_policy
/usr/local/www/nextcloud/apps-pkg/photos
/usr/local/www/nextcloud/apps-pkg/privacy
/usr/local/www/nextcloud/apps-pkg/provisioning_api
/usr/local/www/nextcloud/apps-pkg/recommendations
/usr/local/www/nextcloud/apps-pkg/serverinfo
/usr/local/www/nextcloud/apps-pkg/settings
/usr/local/www/nextcloud/apps-pkg/sharebymail
/usr/local/www/nextcloud/apps-pkg/support
/usr/local/www/nextcloud/apps-pkg/survey_client
/usr/local/www/nextcloud/apps-pkg/systemtags
/usr/local/www/nextcloud/apps-pkg/text
/usr/local/www/nextcloud/apps-pkg/theming
/usr/local/www/nextcloud/apps-pkg/twofactor_backupcodes
/usr/local/www/nextcloud/apps-pkg/updatenotification
/usr/local/www/nextcloud/apps-pkg/user_ldap
/usr/local/www/nextcloud/apps-pkg/user_status
/usr/local/www/nextcloud/apps-pkg/viewer
/usr/local/www/nextcloud/apps-pkg/weather_status
/usr/local/www/nextcloud/apps-pkg/workflowengine
saw other post but got lost identifying the group the sample said should do this: chown -R “user:group” /usr/local/www/nextcloud/apps-pkg