It depends on the camera, Dennis. I have two Nikon bodies that are equipped with mechanical shutters. I also have a mirrorless Nikon that doesn't, and I am amazed at the capability of that mirrorless in dark places. We went on vacation to Alabama in November of 2021 and visited a couple of old forts on Mobile Bay. At Fort Morgan on the east side of the bay, there are some fortifications that aren't a part of the main fort. In some places there, the magazine rooms were in something like 100 feet or so and then took two left turns to where the powder and such were stored.
To the naked eye, that "storage" area was completely dark, and looking through the viewfinder, it was also very dark. My camera couldn't get enough light to even focus, so I "half pressed" the shutter button to get a laser on the camera to light the background just a bit and then manually focused the lens. Then I took the picture, and this was the result of photographing a "black" room.
Needless to say, that black square in the back was totally invisible to the naked eye. Until I saw the picture after taking it, I didn't know that was even there.
