I guess this is software issue because few months back Note 9 and several devices with oled display faced same issue. Do send a report to customer care
To resolve the issue kindly follow the given below steps:-
1. Display brightness level:- Kindly set the device display brightness in auto mode (If available). Steps to adjust brightness in auto mode: Swipe down on the home screen to open notification panel>Turn on Auto brightness.
2. Reset the device:- Settings >General Management > Tap on Reset. Note: Before reset make sure to have back up of the data via Smart Switch Mobile App (Install Smart Switch App > Open > Click on Memory Card Icon >Back Up option > Choose the data for Back up > Back Up).
If the issue still persist, kindly register your concern in Samsung Members app along with screenshots, short videos and error log file(Samsung Members app > Get help > Feedback > Error report/ask question). Note: Please send device log files within 15 minutes of issue occurrence along with the exact issue details.
Please perform the below mentioned steps to resolve the issue:
* Check device in safe mode: Press and hold the Power key, when Power off icon appears > Press and hold the power off icon. To exit safe mode: Restart your device.
For further assistance, register your concern in Samsung Members Application (Open Samsung Members Application > Get help > Send Feedback > Error report/Ask questions).
