Is this a defective monitor or a normal thing on OLED Monitors?

I just bought a new OLED Monitor Asus rog XG27AQDMGR and I noticed a line appears on some colors on the left side of the screen (colors that include gray like #0F0F0F and #191919).

I have contacted the customer support from where I purchased the monitor from and they took the monitor and did some tests and then they said its completely fine and this line diminishes over time but I don't really trust what they are saying because it looks completely off.

Yesterday I played RE8 and its full of dark scenes and the screen becomes completely washed and line on the left becomes absolutely visible.

So I really don't know what to do to prove them wrong and this is a defect monitor so they replace it, I haven't found any monitor tests that really shows this problem over than setting the background color to those and the line appears on the screen.

Help is really appreciated :).

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