Prior to a previous issue I had with the black level, which I solved due to a screen overlay issue, I recently encountered a similar problem again where the black level was not truly black and appeared more like an LCD TV display.
It was pretty obvious what the issue was this time, as I had been adjusting the eye comfort settings quite a bit due to shift changes. It was coming on while I was working, causing the screen to noticeably yellow, as it makes it easier on the eyes at night.
If you have eye comfort set to maximum, you will find that your screen won't blacken fully, resulting in a grey instead of black effect.
So, if this happens to someone in the future, just check the eye comfort settings and reduce the color temperature option or turn it off, and your phone will have OLED black quality again.
I Hope this helps someone, its been my first post in a while but hopefully I'm back.
