Hi Stephan S. after hours of work, i think i found a solution:
Go to <YOUR DOMAIN URL>/wp-admin/theme-editor.php
Does it say: you dont have access?
If so do this:
Log into your webhotel controll panel (not wordpress) and go to file manager. Locate the file named wp-config.php.
**( the direct path ftp.< YOUR DOMAIN URL >.wp-config.php
)
Then change the file using file manager.
The only change that must be done to the code is this:
define('WP_DEBUG', true);
must be changed to
define('WP_DEBUG', false);
When this is done, save changes to the file.
Visit your wordpress admin site, and the advanced code editor will be in your appearance > editor
enjoy ??