@Saul1: Yes, @Guest is correct. What means the problem is not that "only magentacloud.de remains", as that is expected. The problem must be elsewhere.

We need more details (exact error message, or even better a log file) than "session fails". Can you connect with the same login details using any other WebDAV client? If you can, post its log file too.

For the URL, it micro manages it for you and splits it off to an advanced settings path, so its actually still used: How to connect to a server that does not allow an access to the root path?

In GUI, you do that by filling the path (e.g. /dav or /bucketname) to Remote directory box on Directories page of Advanced Site Settings dialog. Particularly with WebDAV, a handy shortcut is to paste a full URL (https://www.example.com/dav/) on Login dialog. WinSCP will parse the path out of the URL automatically.

Hello,
when I enter https://magentacloud.de/remote.php/webdav under Host name only magentacloud.de remains and login for the session fails. What is my fault?
Thanks
Wolfgang