However, when exporting and uploading to the web space of the hoster’s server, how is it ensured that the previous domain name for the local website localhost:xxxx is replaced with the URL of the online website www.my-club.de and thus the website works online with the URL as well?
When you upload your site to your hosting provider, they should be running a search & replace behind the scenes to swap the Site Domain throughout the database from the Local version to the live version you’ve indicated.
Please let me know if you have any more questions!