iPhone 12 mini brightness issue

Azn-M,

Thanks for confirming that. Here’s another condition that could cause it:

"If your device gets too warm

If the interior temperature of the device exceeds the normal operating range, the device will protect its internal components by attempting to regulate its temperature. If this happens, 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, the 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."

Keeping iPhone, iPad, and iPod touch within acceptable operating temperatures

If the issue persists, please reach out here for additional support: Get Support

Have a fantastic rest of your day!

Hi there Azn-M, 

It's great to have you in the Apple Support Community. We understand that you display appears to be adjusting itself, even with auto-brightness off. We’re happy to help.

Another feature that could cause this is True Tone. “It uses advanced sensors to adjust the color and intensity of your display to match the ambient light, so that images appear more natural.”

Adjust the brightness on your iPhone, iPad, or iPod touch

You’ll find the settings to enable or disable it by tapping on Settings > Display & Brightness. Please keep us posted.

Take care.