Hi romeo2903,
Backlight level varies depending on room light conditions, from around 20% up to 100% in daylight conditions - my 12,9 practically always lives on stand on a mini-desk in our tiny home/living/sleeping space ( a laptop would be too bulky and noisy with its fans ). I have accepted this still small issue as “normality”.
I understand that there is a weak spot around the backlight edges where the lamination layers tend to delaminate due to everyday mechanical stresses and even the tiniest misalignment of these layers causes uneven light distribution, brighter close to the leds.
My screen had been 100% ok during the first 18 months of ownership and then my issue developed suddenly and fully in about 2 months and has been stable during the past 11 months. I contacted the local service center, they said “sent it so we can decide at our discretion” but since the best I could hope would be a refurbished unit of unknown history (probably displaying a similar flaw over time), I decided to keep my babied unit despite this flaw - if I ever spent that much on any Apple imperfect perfect product, it will take much convincing to ever do that again. Maybe until this unit dies there will be a proper Android alternative but until then this unit stays.
I hope yours fare better but if I was moving mine around I would expect the flaw to get worse over time - it is a weak point.
A PATCH APPLE COULD APPLY would be 5% crop of the displayed screen so the issue would be invisible inside a small black margin around the visible part of the working screen but they shall never do that, accepting their design was flawed, since this would raise a legal compensation storm, nevermind Samsung’s mocking ads (one company with even worse mishap record pointing fingers instead of just shutting up).