Things (eventities) have properties. Properties are characteristics of the thing. Properties are either essential or accidental to a thing. Accidental means that it could be otherwise without changing the essential nature of the thing. Essential characteristics determine the whatness of the thing.
Quora answer: Is existence a property?
Existence properly speaking is not a property or characteristic of a think, but is rather a standing. Being is another standing. A standing means a way of approaching a thing rather than something inherent to the thing itself. So a thing is not changed essentially by whether it exists or not. A Dodo bird which is extinct is not changed essentially by the fact that it does not exist, i.e. it cannot be found anywhere.
So asking whether existence is a property is a category mistake. However, in logic existence is treated as a property because we write a backward E as a uniary operator to signify that something actually exists. We owe this convention to Charles Peirce. But existence i something that we confer and not something intrinsic to the thing itself. So I think that is where the confusion comes from.