The universe is not sufficiently old to have Black Dwarfs yet. Those are white dwarfs that have radiated the vast majority of their residual heat and are no more visible in the visible spectrum. The oldest white dwarfs known are from the infancy of the universe, around 11 billion years old and they have cooled to 3900 K, that means they are glowing orange (maybe that would be a neat addition to Space Engine: some very unfrequent "orange white dwarfs"). The time to reach temperatures so the white dwarf no longer glows in the visible spectrum is debated but the smallest estimate gives 100.000 times the age of the universe.
They are not 100% confirmed (nothing in science is 100% in fact) but yeah, I mean, theoretically they should appear sometime in the far future (even the sun should become one in 1015 years). The thing is that obviously no black dwarf has been observed so no confirmation at all. In fact that makes sense with our estimates of the age of the universe. If you where to put black dwarfs in SE then to make it realistic you should change the whole galaxy (since Milky Way, Andromeda and Triangulum would be fused by that time), the solar system should be erased (or almost all planets changed in to other kind of objects), the large scale structure would have to change and galaxies be way more sparse between them, the galaxies more yellowish and with less bright star forming regions (older stars), stars with higher metallicities are the only stars you would see, in fact since this time would be after the end of the stelliferous era there would be no more star formation, at this time the vast majority of planetary orbits (those planets who survive around stellar remnants) would have decay or been ejected, so no more planets to explore around stars, and the universe you could explore should not extent farther from the Virgo Supercluster of galaxies (galaxies farther away would be outside our hubble sphere by now), so you could still explore around a million galaxies. But not all of this would be dark and unfunny, you would have probably new exotic objects and phenomena pertaining to this new era of the universe.
So no, better to not include black dwarfs sicne they dosen't exist but when they will the universe in SE would look completely different. But yeah we should include orange white dwarfs somewhere right?