If you notice that your iPhone brightness changes even though you have your Auto-Brightness disabled, this could mean that your device is overheating. The phone automatically dims the screen to regulate its internal temperature, causing an adjustment in the display's brightness. Your iPhone may also have a feature called "Night Shift" activated, which can affect the brightness of your screen. This feature will automatically adjust the warmth of the color of your screen depending on the time of day. Again, this is designed to make your screen readable in various lighting conditions. You can disable Night Shift following these steps: 1. Navigate to your "Settings" icon and tap it. 2. Scroll down until you reach "Display & Brightness" and select this option. 3. Find "Night Shift" and slide the toggle to the left to deactivate it. 4. Navigate back to your "Home" screen.