Login data is not possible, because I work on localhost.
To clearify: I have in my Joomla folder a folder "FCL" with subfolders. As workarount I put into the folder "images" a folder "FCL2".
As you can see from the screenshot.
Joomla configuration is:
Path to file system = FCL
Path to images = FCL/bilder
In Joomla Content -> Media: FCL is top level
In Joomla Editor, selecting an image: starting page is images. (No access to FCL possible)
In Site Template Styles -> Template Options -> Basics: images is top level (No access to FCL possible)
https://drive.google.com/drive/folders/1cxjeDUjDUCzOP9vFZ4unt09St3gveS8W?usp=sharing
So, only in Content -> Media the path is seen relative to the Joomla directory. The other cases show the path relative to the images directory.
Emptying Joomla cache does not solve the problem.