Why are the photos taken by my SLR particularly dark? Are the components of the SLR broken?

Of course, it's not the camera, but the illumination of the scene is very low. Your exposure settings don't meet the illumination requirements, so the photos will be underexposed.

Generally speaking, if you want to shoot enough exposure film indoors, you need the support of a large aperture lens, such as a small spittoon with a size of 50 1.8. Your lens is a ferrule. When the focal length is lengthened, the aperture will be closed to F5.6, which is already relatively small and cannot meet the exposure in dark environment. If you don't want to change the lens, you can shorten the focal length, such as shooting with 18mm, so you can use the F3.5 aperture. Although it is not big enough, it will be much better to use high ISO.

From the above picture, the second picture uses a short focal length, so the aperture will be larger and the brightness will be higher under the hood.