Invention preceding understanding is the norm, not the exception. We created fire before understanding chemistry, and we constantly use pharmaceuticals without really understanding how they work. Invention first, then theory comes along to explain and generalize.
For all we know, sentience is a necessary side-effect of semantic processing of any kind, in which case LLMs already have a form of sentience.
So yes, you're right that we don't understand our own sentience. In fact, we understand so little that it could literally be staring us in the face right now and we don't realize it.
Some people claimed that "creativity" (another rather nebulous term) was a uniquely human trait, and machines could perform tasks that require this. But recent generative AI models have started to make people question that position.