Since this has costs me some time and I am still confused why GetValueAsString is giving back not the value only.
What i ended up is doing a .RightChop by the name +2 of the enum to get the Value only.
FString FileEnding = UEnum::GetValueAsString<EDesiredImageFormat>(WriteOptions.Format).RightChop(21);
isnt there a easier and dynamic soltuion to only get the value as sting not the whole Enum::Value ?