Physics should not or cannot answer such a question: it belongs to philosophy, which guides all sciences, and all arts, and all thinking.
A human has a limit of knowledge. So, subject to the limited ability of the human to comprehend something, an objective reality is said to exist in the object itself, regardless of whether one or another human knows it or not,and regardless of what they may think or not think.
Ontology is a branch of philosophy that deals with the issue of existence. An object may be said to exist if it invades the senses of ordinary people, and publicly, so that they are unable to deny its existence. This undeniability is related to the later methodological issue of falsifiability. Put your hand in fire and deny its existence. If you are able to say that it does not exist, and if all other people say that there is no fire, then there is no fire. In short, if there is fire, you cannot deny that it is there.
The other part of objectivity is that the object remains the same regardless of who perceives it. So if there indeed is a black dog, all people who see it must agree that it is a dog, it is a black dog, and it has a weight of 46 pounds and a height of 26 inches and so on, using the same shared language to call a color black if it is black, and to measure a height in the same units so everybody gets the same height. If somebody says that there is a dog, while somebody says there is a goat, and one says that it is black and another says that it is grey, and one says that it is 97 inches tall and another says that it is 4 inches tall, then there is a problem: there is no object. All or some people are telling lies. If there is an object, everybody who sees it must find the same thing: same name, same category, same measurement.
Physics is possible only after the philosopher assures that objects exist. Physics studies the behavior of inert objects according to natural laws that govern the behavior of the particular object. It does not have to prove that the object it examines exists.
If there is someone who thinks objects do not exist, kick them on the nose and pour keroseine on their tongues and ask: what is your opinion now? Does my boot exist, does your nose exist, and does keroseine exist?