So I compared in safe mode and it seems like it might be a teeny bit brighter.. But not much. So how the heck do I get to this device health services app? Is this the same thing as like the device diagnostic program?
I already explained to you how to do this (I checked on my tablet with Android 12 and it is almost the same as in Android 9):
1. Go to Settings
2. Tap on Apps
3. Tap on magnifying glass to enter search mode
4. Type Device and look for Device Health Services app
5. Tap on Storage
6. Tap on Manage storage
7. Hit Clear all data
8. Enable/Disable Adaptive brightness
Test your phone to see if it was fixed.
I'm afraid I honestly have some kind of hardware issue. I have a feeling my screen is slowing burning out or something to that degree.
This might be also one possibility, unfortunately.
There are two more tests to try:
1. Open your phone dialer and dial *#0*# ; You will get a menu of hardware tests you can try (only the first 3 are relevant for the display RGB). There is also a touch screen test here but it's tricky to stop it.
2. Open Samsung members and tap Diagnostics. You will be able to test the touch screen. This the only test for the display.
Unfortunately, none of these tests will give any info on your phone's brightness problem, but it doesn't hurt to try.
This is all I have on brightness. If nothing helps, then only a repair shop could be your solution.