I don't think there's is much of a similarity between those two. useRef is a react hook whereas onBlur is an event handler.

userRef allows you to create mutable objects within a react functional component, so you can have a value that persists across renders. The hook returns an object with a current property where the mutable object reference lives. Usually it is also used to create a reference to the dom node of a certain element, and this way you can work imperatively with the dom node by doing for example yourRef.current.focus()

onBlur on other hand is an event handler that you can attach to elements (usually inputs) to call back on the event when the element loses focus. I think of blur as the opposite of focus.