Solution: Don't work in a dark room with the MBA on high brightness, while looking at a dark/black background!
We can drive ourselves crazy looking for — and finding — minor imperfections that show up only in extreme circumstances. It's not worth it. You'll end up with OCD or make it worse.
I have the M2 version of your laptop and the display is wonderful. (Ignoring the notch, that is! 😁)
But I definitely won't test my MBA in a dark room with the backlight turned way, way up while looking at a photo of a black cow standing in a dark field on a moonless night at midnight! 😁
I'll wager that many 15” MBAs, M2 and M3, will show what you've unearthed. But, unless it's a distraction in your regular use, I’d ignore it.
Indeed, I can't even see the issue in your photo!
Oh, wait! You mean the slight, tiny barely noticeable white vertical dash in the bezel, not the display. If it bothers you — and you're still in a return window — and haven't installed a lot of stuff — return it and get two new laptops.
Or course, they could have other issues… So, if these laptops are, otherwise, good, then ignore it. Like the notch, which is far worse, and far more in your face, that little white dash, only seen in real darkness with backlight way up, should be easily ignored or remain invisible (unlike the notch) in regular use!