Let's see an example.
I see the kind of posterisaion that's normally caused by too low a quality setting in the Export dialogue.
You haven't included any Exif in the image though (always do that in these situations); and this is a PNG rather than a jpeg (we need to see an actually exported jpeg, not a screen print). so it's hard to be sure.
What value is the Export "Quality" slider at?
Thanks for your comment !
When i export it, then the exported file quality is ok.
It is only the problem when displaying the image while working in LR.
Therefore i had to take screenshot as png to show the issue/
Especially for blue sky landscape it makes it hard to edit when the sky looks so strange.