You are mostly empty space. Every atom in your body is very tiny compared to the relatively vast spaces between it and its nearest neighbors. And the same goes for every "solid" object you ever saw.
But when you look at yourself in a mirror, the number of atoms you see is so incredibly vast that you don't see the spaces between them but instead think that yhour body is a solid object.
And probably the wavelengths of visible light are too long to fit between atoms and so get bounced back from the surface of your body.
That is not the case with the galaxy, since the spaces between stars in the galaxy are wide enough for all wavelengths of light to pass through instead of being reflected.
But if you look at our galaxy from a distance of about one million light years, the average separation between stars of about 6 light years will be a very small angle. I believe that at one million light years distance, one arc second will be about 4.848 light years wide.
The maximum angular resolution of the human eye is 28 arc seconds or 0.47 arc minutes, this gives an angular resolution of 0.008 degrees, and at a distance of 1 km corresponds to 136 mm. This is equal to 0.94 arc minutes per line pair (one white and one black line), or 0.016 degrees. For a pixel pair (one white and one black pixel) this gives a pixel density of 128 pixels per degree (PPD).
So at a distance of one million light years the smallest detail a human could see would be 28 arc seconds, or 135.7 light years wide. So such a smallest possible thing you could see would be a square about 136 by 136 light years wide, and possibly containing about 350 stars in a single layer and all the vast interstellar spaces between them.
Furthermore, galaxies are not a single layer deep. Depending on the size of a galaxy, the distribution of stars within it, and the angle from which it is viewed, a viewer might see tens, hundreds, or thousands of layers of stars one behind the other. The stars are not arranged in any sort of regular lattice pattern, but orbit around the center of the galaxy in separate orbits and their relative positions slowly change, thus making their relative positions random.
Thus the empty spaces between stars in the outermost layer of a galaxy will show the light of stars farther behnd them.
So when you look at galaxy from a distance of one million light years, the smallest part of the galaxy you can see will have the light of hundreds or probably thousands of stars blended together with the black space between them to make a pale grayish light.
The farthest objects which humans can see with the unaided eye are the Andomeda Galaxy M31 about 2,540,000 light years from Earth, and the Triangulum Galaxy M33 about 3,200,000 light years from Earth. Since they are several times a million light years away, the smallest part of them which can be seen with the unaided eye will combine the light of even more thousands of stars together.
Astronomers have photographed galaxies tens of millions, hundreds of millions, billions, and tens of billions of light years distant. With astronomical telescopes they can detect some individual stars in galaxies tens of millions of light years away.
But any photograph which shows an entire galaxy will show the light of millions or billions of stars blurred together into a blob of light.