We obviously can, otherwise where do our myriad of complex concepts, many of which aren't empirical, come from? How could we have modern mathematics unless some thinker had devised the various ways of conceptualizing and manipulating numbers? This is a very old question [1] with a number of good answers as to how a human can [2].
As you link to The Copy Principle: it, or at least that summary of it, appears to be very much what AI do.
As a priori knowledge is all based on axioms, I do not accept that it is an example of "something truly novel, not related to anything it's ever seen before". Knowledge, yes, but not of the kind you describe. And this would still be the case even if LLMs couldn't approximate logical theorem provers, which they can: https://chatgpt.com/share/685528af-4270-8011-ba75-e601211a02...
> come up with something truly novel, not related to anything it's ever seen before?
I've never heard of a human coming up with something that's not related to anything they've ever seen before. There is no concept in science that I know of that just popped into existence in somebody's head. Everyone credits those who came before.
1: https://plato.stanford.edu/entries/hume/#CopyPrin
2: https://en.wikipedia.org/wiki/Analytic%E2%80%93synthetic_dis...