Thank you for your answer and sorry, that I did not mention my setting.
I am connected via Remote Desktop from Windows 10 to the named Ubuntu machine. Nvidia-settings worked as expected some days ago. But as I mentioned, I installed different cuda versions and I think there might be some paths conflicts which might cause the problem. Is that possible? How does Nvidia-settings know from where to get the information it shows?
Concerning the remote Ubuntu machine: Is it necessary that a monitor is connected to that machine so that Nvidia-settings shows the right information?