How do I make my iphone 6s screen brighter, AFTER already adjusting the brightness all the way in settings.Its still not bright enough

How do I make my iphone 6s screen brighter, AFTER already adjusting the brightness all the way in settings. Its still not bright enough

Maximum brightness is maximum brightness. That's as far as you can go.

But many replacement screens aren't as good as the originals and aren't as bright. Also screen protectors tend to reduce contrast and on a Gorilla Glass screen on genuine iPhone screens from the iPhone 5 and onwards aren't necessary, I carry my phones in my pocket with keys and change and none with a Gorilla Glass screen has ever chipped or scratched. I've also never had any of them crack either but most screen protectors can't guard against that anyway.

If the screen is genuine then it may simply be fatigued due to age. If so sell your phone and buy a replacement; a genuine Apple screen swap will cost more than selling and replacing.