The brightness of always on display is not based on your phone brightness The brightness of it automatically adjust the surroundings Wana check Keep our hand on its sensor the always on display brightness will increase keep your hand for a 8 to 10 sec you'll see the results ....
Please perform the following steps to resolve the issue:
1- Reset the settings via- Settings > general management > reset > reset settings.
2- Check the mentioned issue in safe mode.
3- If issue still persists, create data backup and reset the device.
For further assistance, register your concern in Samsung Members Application (Open Samsung Members Application > click on “+“icon > send feedback > error report/ask questions).
