There are many depth cues other than binocular parallax, so people with one eye can still judge depth, just not as well.

Examples of monocular depth cues include:

Relative size, or absolute size of familiar objects: the farther away something is, the smaller it appears, and this can be used to either compare similar objects that appear different sizes, or to judge the distance of an object whose size is familiar.

Texture gradient: basically, this is relative size applied to the fine detail of texture. Imagine a gravel road, for example; its apparent texture becomes finer the farther away you go.

Motion parallax: things moving at familiar speeds have slower apparent motion the farther away they are. Or, when you are moving, things farther away from you have slower apparent motion.

Overlap: closer objects obscure farther ones.

Elevation to the horizon: things farther away tend to be nearer the horizon.

Accommodation: Your eye changes shape via muscular action in order to focus on objects, and the shape depends on the distance to the object.