Gray tones are not displayed on the external monitor?

I'm done. I connected my Dell Latitude 5500 laptop to my PC monitor today because my PC stopped working on Saturday. However, I have a strange phenomenon.

On my externally connected monitor, no gray tones are displayed or no real white, depending on how you interpret it.

I've tried everything:

Monitor to factory settings

Graphics driver reinstalled

Another HDMI cable used

PC restarted

Resolution changed

Etc.

If I connect the laptop to my Samsung TV, the colors are displayed, same on the TV in the bedroom.

In order to rule out a defective monitor, I connected another monitor of the same construction (I have 2 monitors on my PC) and I also connected another laptop to the monitor and strangely enough it worked without any problems.

I really don't know what to do next… Anyone else have any advice for me?

If no gray tones are displayed, the contrast is set too high.

Search test reports with gray stairs,

Decrease contrast,

Readjust the brightness so that differences can be seen in both the light and the dark parts of the brightness levels.

The setting must be made on the monitor.

Can also be a defect or weakness of the background lighting

I know that too.

They have set a different color temperature or

There's not much you can do about that

Maybe the https://www.heise.de/...18034.html is activated?