Have a 55” curve 4k tv that has power lets out all symbols that its working properly but the picture is very dull like not visible even pitch black room.. possible fix?

Could be a power supply of a panel. Also could be a bad connection somewhere. Bring it to me to check it out. There is a $65 estimate

I would take it in and let them check it out it could be something as simple as bad caps on the power supply board or an led driver board

Possibly. It could be a simple board repair, to possibly a panel. I suggest bringing it in, so they can look it over properly.