my iphone SE2020 keeps dimming all by itself

Hi Hankie,

Welcome to Apple Support Communities! We're more than glad to help with your question.

Your iPhone's display may adjust the brightness automatically based on ambient lighting conditions. The following guide explains all about how this works in detail, including how to turn this feature off. Refer to the section titled, "About brightness levels":

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

It's important to note also that even if this feature is turned off, your iPhone's display may dim if the device becomes warm, in order to protect its internal components from overheating. For example, if your iPhone is used in direct sunlight, the brightness will be higher at first for easier viewing. However, if it's kept in the sun and warms up, the brightness will dim.

This Knowledge Base article has more details:

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

Hope this helps. Have a great day!

Hi Hankie,

We're glad to hear you were able to get this resolved. Thanks for keeping us updated.

Take care!