nvidia – Ubuntu 18.04 KDE / Gnome settings no longer see some monitor modes

I recently updated my system from Ubuntu 16.04 to 18.04 LTS. I have a Lenovo W530 notebook with an NVidia Quadro K1000 graphics set. I have 2 external monitors, one is an older Dell 1900×1200 and a new 27 "Acer monitor, the 27" monitor supports 3840×2160, but I prefer to run it at 2560×1440 in portrait orientation (turned to the right). I usually use KDE.

In 16.04 I could use the KDE settings to set the resolution to 2560×1440 and the rotation, or I could use the NVidia X server settings to make the same setting. Under 18.04 in the KDE display settings and also in the native Ubuntu display settings, however, only the modes 3840×2160, 1024×768 and 640×480 can be seen.

How do I set the 2560×1440 display mode?

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