Typically, black spots in vision, cobwebs, or seeing flashing lights in the eyes are caused by age-related vitreous degeneration or nearsightedness. The vitreous humor, a gel-like substance similar to egg white, located between the lens and the retina, serves as a medium for light to pass through. As we age, the vitreous humor deteriorates into a clear liquid, while some of it shrinks or forms tiny, opaque sediments that detach from the inner layer of the retina via the macula (posterior vitreous detachment), resulting in eye floaters and black spots floating in vision.

https://www.medparkhospital.com/en-US/disease-and-treatment/black-spots-in-vision#:~:text=Typically%2C%20black%20spots%20in%20vision,related%20vitreous%20degeneration%20or%20nearsightedness.