It's just rare in nature.

In fact, it cannot exist in nature for a long time.

Let's analyze:

Since it is univalent Cu, that is, Cu+, it can't exist alone from the beginning, let alone be a simple substance.

It can only be a compound.

A typical substance is copper hydride, i.e.

CuH, where Cu is monovalent,

As a typical nonmetallic element, H, when combined with Cu, gains electrons and becomes-1 valence.

This is an example of the existence of monovalent copper.

In fact, this substance is a topic of a national high school chemistry competition in a certain year. I've done it, so it's better than.

Relatively clear.