What does a fixed-focus lens mean in photography? What is the effect of the photos taken by the fixed focus lens? What are the benefits?

There is a ready-made answer to this question online.

As the name implies, the fixed-focus lens has no zoom function. The design of fixed-focus lens is much simpler than that of zoom lens, but the general zoom lens will affect the imaging when zooming. The biggest advantage of fixed-focus lens compared with zoom machine is its fast focusing speed and stable imaging quality. Many digital cameras with fixed-focus lenses have clear and stable images of moving objects, very accurate focusing, delicate pictures, very slight graininess and relatively accurate metering.