These were some quick ways to fix the iPhone screen dims automatically issue. Wrapping Up- (Solved) iPhone Screen Dims Automatically Visit an authorized service center and let them diagnose the phone to know the exact cause.
Restart your iPhone to clear out any temporary glitches.If you have followed the above solutions yet nothing seems to be working, there are some other options you can try: Other Ways to Stop iPhone from Reducing Brightness On its Own If your battery is already worn up significantly, here are some handy tricks to save battery on iPhone. So, try to keep it in the ideal temperature range. Using the iPhone in very hot conditions can permanently shorten battery life. To cool it down, turn it off or stop using it for a while and move it to a cooler environment. So, if your iPhone has reduced its screen brightness automatically, check if the phone is hot. If it gets too warm, it may try to regulate the temperature by slowing down or stopping charging, throttling performance as well as dimming down the display. High ambient temperatures like using the iPhone under the direct sun can cause it to heat up. OR, open your iOS control center, and tap the Low Power mode (battery) icon.
