Much of what is new to us is incremental progress over something older, some foundation that provides very large shoulders to stand on. There are plenty of ways to come up with novel ideas that don’t require absolute novelty. In fact, it’s probably impossible to have any entirely novel idea, because every idea is embedded in a world of preexisting ideas that can’t really be separated. Unless your worldview is completely alien to this world (and therefore, pretty useless in reality) it’s not going to be 100% new. It makes more sense to build on what exists than to try to reframe everything all at once.
One way to do new things without inventing a universe from scratch is to find connections between two fields of interest. For example, if you happen to be really into Bach’s music, and also into studying the Fibonacci sequence, you might try to make some music in Bach’s style based on that sequence. I think much of the big, valuable, interesting new work in the world comes from these confluences. Plenty of people know about plenty of things, but because the variety of things to know about is large, it’s much more rare that anyone in the world has a deep interest in a pair of your deep interests than that they share one of your deep interests. The combinatorial explosion of possible pairs of things to know a lot about is fertile ground for ideas unique to an individual who just happened across the right set of ideas.
Another fast path to good novel ideas is to change the level of abstraction you’re operating on. If you’re working on some specific mathematical proof, one good way to make progress is to see if you can generalize the objects you’re dealing with. If you find a proof at a more general level, not only does that imply a proof for the specific sublevel, but it might also provide value for other subproblems that you didn’t even think of ahead of time. Generalization has pretty strong powers.
You can also just start with an extremely small niche idea, and eventually grow the numbers of people who might be interested in it. In the marketplace of ideas, this is sort of the path to expansion. The tiny core idea is what has to be novel, but a huge fraction of the actual work to be done comes from growing the community around it. Helping this novel nugget grow and evolve may not itself be novel, but it does help with the spread of an idea to people for whom the idea is completely new.
Sometimes the way to something new runs through being more specific. If you’re working on some problem at a general, overview level, there may be details lurking under the surface that are being overlooked. By being willing to change your level of abstraction and dive into these smaller ideas, you may find ways that the specific details of a problem change its character, and lead to novelty.
Having new ideas isn’t necessarily about just sitting around until a fully-formed light bulb shows up in your head. In fact, I’d bet this is almost never what happens. Ideas are malleable and change over time, so connecting pairs or abstracting single ideas is often a good strategy for finding new and valuable ones. The lack of novelty just springing up for us isn’t a drawback, because it provides us with more structured ways to have new ideas if we care to try.