Ok I have a iPhone XR and display brightness changes by itself,but I have it turned off so it doesn’t but it still does! So annoying cause it goes darker when I’m in darker place it’s suppose to go brighter right? And put the battery percentage back!

There's no way to display the battery percentage on the Lock or Home screen, because there's no enough space for that. You can access it from the control center.

Speaking of the auto-brightness.

First, try to reset all settings on your device under Settings > General > Reset.

If this doesn't resolve your issue, restore it using the instructions from the article below:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

If still no luck, schedule an appointment at a Genius Bar or the nearest Apple Authorized Service Provider for them to take a look at your iPhone.

You'll have to turn off Auto-Brightness if your iPhone keeps dimming and you want it to stop. Open Settings and tap Accessibility -> Display & Text Size. Then, turn off the switch next to Auto-Brightness.