All the problems can be solved when you install the MonitorDDC app. The prog can detect my SP3 screen (120QL01) then provide ability to change the LCD brightness (and show brightness level in real time if you or other softwares change it). It also provides features of rotating the screen and assigning keyboard shortcuts to a variaty of screen and volume changing.
The app's link: https://clickmonitorddc.bplaced.net/