My IPhone 13 Pro max display

Probably you have turned on Night Shift

• Open Control Center. Firmly press the Brightness control icon, then tap to turn Night Shift on or off.
• Go to Settings > Display & Brightness > Night Shift. 2 On the same screen, you can schedule a time for Night Shift to turn on automatically and adjust color temperature.

Please see the pic below and check the status of your settings on your device.