it seems that Magentacloud has still technical problems at the moment (today I also have issues again - yesterday it worked perfectly for me). They are “working on this”:
Die neue MagentaCLOUD | Telekom (telekom-dienste.de). Magentacloud update seems the same desaster as the move from Mediacenter ot Magentacloud some years ago.
About the settings: Simply login into the web-client and navigate to the “Sitzung/Geräte” settings. There create a new “Sitzung”. A password is generated automatically and is shown until you click “Erledigt”. I think you can change the Username, but you can also keep it.
After Clicking “Erledigt” there no way to show the Password again. So if its lost you have to choose “Widerrufen” (not delete(!) - this will remote erase the data on the device) for the Device from the list and create a new one Password as described above.
Remember to create a unique “Sitzung” for every app/device you want to connect (for example one for Duplicati and one other for Windows-Explorer-Drive, another for your mobile app and so on).