Some rumors suggested that the peak brightness could reach up to 2500 nits
Recently, the leaker @ShrimpApplePro suggests that the iPhone 15 Pro Max could be getting a brighter display made by Samsung. Where the next-gen display panel can reach up to 2500 nits of peak brightness.
Moreover, the display analyst Ross Young states that he has not heard anything about this feature would be implemented on the next iPhone model. Keep in mind that the brighter the screen could result in a shorter battery life.
The 2500 nits of peak brightness feature could probably be applied to outdoor brightness and will be lowered in normal conditions to prolong the battery life and display longevity. However, the iPhone 15 Pro launch is still months away. Who knows if Apple decided to hold back the feature for another iPhone Ultra model?