Nvidia A5000 to LG OLED C9 - Top-Horizonal line

Hi all.

I am trying to connect my new Nvidia A5000 (only DP outputs) to my LG OLED C9.
I know the card can do 4K@120Hz and also that the TV can display this.

But (1) the resolution doesn't show immidiately when I connect the cable to the dongle (the cable is also Club3D)
(2) When I try manually inserting the resolution in the Nvidia driver dialog box I get this strange thin horizontal line at the top of the TV. and windows task-bar is chopped at the bottom at the same thickness of the line at the top.

If I reduce the refresh rate to 60hz - the line gets thinner - but still there.

help?