Big problem iphone 13

Hello gangesh1825,

Welcome to Apple Support Communities. 

We understand that you’re experiencing unusual heat and display brightness isn’t as expected. We are happy to help.

These steps may help. We recommend the steps here: If your iPhone or iPad gets too hot or too cold - Apple Support

"Your device might get warm

You might notice that your device feels warmer when you:

• Set up your device the first time
• Restore from a backup
• Wirelessly charge your device
• Use graphics-intensive or processor-intensive apps, games, or features, including augmented-reality apps
• Stream high-quality video

These conditions are normal, and your device will return to a regular temperature when the process is complete or when you finish your activity. If your device doesn't display a temperature warning, you can keep using your device.

If your device gets too warm

iOS and iPadOS devices have built-in protections to prevent overheating. If the interior temperature of your device exceeds the normal operating range, your device will protect its internal components by attempting to regulate its temperature. 

Avoid these conditions and activities because they might change the performance of your device:

• Leaving your device in a car on a hot day.
• Leaving your device in direct sunlight for an extended period of time.
• Using certain features in hot conditions or direct sunlight for an extended period of time, such as GPS tracking or navigation in a car, playing a graphics-intensive game, or using augmented-reality apps.

If the interior temperature of your device exceeds the normal operating range, you might notice these changes:

• Charging, including wireless charging, slows or stops.
• The display dims or goes black.
• Cellular radios enter a low-power state. The signal might weaken during this time.
• The camera flash is temporarily disabled.
• Performance slows with graphics-intensive or augmented-reality apps or features.

Additionally, if you're navigating, your device might show this alert and turn off the display: "Temperature: iPhone needs to cool down." Navigation still provides audible turn-by-turn directions. When approaching a turn, the display will illuminate to guide you through the turn."

We also recommend the steps here to adjust the brightness: Adjust the brightness and color temperature on your iPhone or iPad - Apple Support

"About brightness levels

iOS devices use an ambient light sensor to adjust brightness levels based on the light conditions around you. The sensor lowers brightness in dark locations and raises brightness in light locations. The auto-brightness feature is on by default.

When auto-brightness is on, you'll notice that the brightness slider on your device moves according to changing light conditions.

To turn auto-brightness on or off:

1. In the Settings app, tap Accessibility.
2. Tap Display & Text Size.
3. Scroll to Auto-Brightness and tap to turn the feature on or off.

If you think your screen brightness isn't adapting correctly, try to turn off auto-brightness and then turn it back on."

Let us know if you have further questions.

Take care.