When a normal star becomes a white dwarf, it is possible that what remains may be very close to having enough mass to produce the gravitational field needed to collapse it and cause a supernova. It would only require a small amount of additional mass to send it over the edge. This additional mass might be collected by interstellar gas. However, a white dwarf can collect material from a neighboring star if they are orbiting each other very closely. Such systems are called binary systems because there are two stars orbiting each other.
White dwarfs are very hot at first and cool over a long period of time.
Those that have cooled enough cannot be seen. Larger stars spend their fuel more quickly and their remaining white dwarfs are more massive and need less material to go supernova. So, if it is a darker white dwarf that will supernova, then it must have been cooling and gathering material over a longer period of time. And if it has been cooling for a long period of time, then it must have formed early in the life of the universe and spent its fuel quickly. And if it spent its fuel quickly, then it must be massive and close to the edge.