May be a burn in. How old is the TV? Was it always there?
In the naked eye it looks like a backlight rather than burn. There is no loss in color and in other colored backgrounds it's impossible to spot the shade only this small spot. The tv is 7y old.
Yes, it's visible on HDMI and areal signal. The shading its impossible to spot on any colours apart of dark grey. The spot is visible on all colours on some of them more than on others. You can also spot another dot especially when you look at white or light grey colour.
Can you send me a private message with your full model and serial number?