Can someone suggest a possibility to export the whole user list to a text file / csv / xlsx .
From the admin GUI there is no export possibility so i am wondering if i can find something directly in the database or export it somehow from the console. ( centos 7 )
Take a look at the Gitlab API. You can use that for getting a list of users in JSON format: Users API | GitLab
After that you could manipulate the JSON data extracted (perhaps extract using Python connecting to the API), then using Python or whatever to then make a CSV file from the extracted data.