Hello Hansi,
Thank you for your message.
First of all, please accept our apologies for any inconvenience this may have caused.
What you are experiencing is expected behavior. When selecting SP Page Builder as the editor for an article for the first time in SP Page Builder on Joomla!, the article must be saved once before the SP Page Builder interface can be initialized.
This initial save allows the system to generate the required data structure and link the article properly with the SP Page Builder editor. After saving the article for the first time, you should be able to click the SP Page Builder button and access the builder without further issues.
We appreciate your understanding. If the issue persists even after saving the article first, please let us know and we will be happy to investigate further.
Kind regards