Ultimately any claim that there exist only combinations of old ideas must tackle this chicken-and-egg problem convincingly. For example- explain art. There was no art until it appeared fully formed and out of nowhere in early anatomically modern humans' dwellings (Neanderthals also had art but it was simpler and it is subject to the same chicken-and-eggness). So where did art come from? What pre-existing ideas were combined to bring it into existence from non-existence?
Btw, since I've had this conversation before- if the answer is that we looked around us in the world and saw things; yes, but we didn't see art. Where did art come from? Where did the idea come from of abstracting shapes and colours so that they resemble the shapes and colours of existing things, without actually being those things, or being composed of pieces of those things? How about numbers? How about writing? How about all our technology and science? Where did those things come from? What did we combine to create them?
Obviously I think that the argument that there are only new combinations is wrong: we are a creative species. We can create new things. Somehow. It would be very interesting to understand how. We have not yet created machines that can match us in that and we can't understand the "how" by studying the machines we have now. By denying the mystery of this our ability, by denying that it is a mystery, by dismissing it and accepting any facile explanation that presents itself in our current era -it's god, it's nature, we're like LLMs- we are making ourselves a great epistemic disservice, denying ourselves the chance to find out what it all means, to understand what kind of creature we truly are.