@Tahir_P7: If you head to the Phone app, dial *#0*# into the keypad and tap on Red, Green and Blue respectively, does the semi-circle appear in any of these screen tests? If not then, to troubleshoot the issue, please try pressing on the semi circle and dragging it downwards, just in case it is a floating notification that is partially off screen. Alternatively, restart the device, then head to Settings > Notifications > Advanced settings > Floating notifications > Off. I can see that you have the Accessibility button activated, therefore you could also try disabling this feature temporarily to see if you notice an improvement. To do this, head to Settings > Accessibility > Advanced settings > Accessibility button, then tap any options with a tick next to them until the stick figure in the bottom right corner disappears.