imac screen display brightness

Hi,

I have an 2019 27'' iMac

Last week, my internal 2TB Fusion drive died and replaced under apple care warranty.

I was surprised to find out that they also replaced my screen which had no issues at all...

now I have noticed that the last 5 brightness bars have no influence at all, I mean that when I use the F2 key on the keyboard, the display is dimming up until the last 5 bars and the last 5 bars are the same brightness...

I use external display as well and I remember that the iMac was way more bright Than the external display and now they have similar brightness...

any suggestions?

Thanks