Don't worry that it's already been done. It has, and it hasn't. It doesn't really matter. Make your art.
The Prize and Illusion of Invention
Doesn't invention feel like such a prize? It's so good to feel like you've contributed something truly original to the universe. That happens, but not often. How often have you had a good idea -- for years even -- that seems so original and different. It is nigh impossible that anyone could have had this same thought! And then you actually meet someone on this Earth of more than 7 billion people that describes the exact same thing. It's uncanny. Why is this always surprising?
We feel like our ideas will truly be worth production if and only if they're a original thoughts and we are the inventor. I love when this happens, or seems to happen, but I think most of the time it's an illusion. We are influenced by so many things around us. Our brains are great at noticing and processing massive amounts of information that our subconscious, at some future point, will produce for us at an opportune moment. It'll seem original, but it'll really be a derivative of all those moments of impression leading up to that instant.
There Can Be More Than One
Part of the reason we want our ideas to be original is that we don't want to just remix what someone else has already done. That's boring, right, and what value are we adding there? That's natural, though many creatives have posited that everything is a awesome -- I mean, a remix.
If there is one of something in the world, that prototype is not also going to be the very last version of that something. There will be iterations by the original creator and others. There will be other variants produced. Do we all drive the same car? Do we all live within the same architecture? No. There are many things shared: a combustion engine or an asphalt shingle. But even these have variants.
No One Has Experienced Your Art
No one has experienced your art yet. You haven't produced it yet. The act of creation expresses the unique combination of the subject to be created and the creator. If you don't make it, the world will never experience it in quite the way that you will offer.
Not everyone on the Internet has heard of everything you've heard of on the Internet. You might reach new people. You might create in such a way that touches a whole new class of people.
The art will stand on its own. It could live as a peer next to many similar works, and that's ok. It will have been created. You will have done it. The experience, the moment in time, the change within you, and the impression upon others are all things that will make creating your art worth it.
So don't worry that it's already been done. It has, and it hasn't. It doesn't really matter. Make your art.