Are you less likely to be accepted to Y Combinator if you don’t know how to make money yet?
If you apply and say “we have no idea how we will make money” you are much less likely to be accepted than if you say “we’re not 100% sure how we will make money, but our initial thoughts are to try X”.
The former demonstrates a lack of initiative and doesn’t make a good impression at all.
YC fully expect that your initial idea for a business model will probably not be the one that works out in the end, but that doesn’t mean you can get away with not thinking about it.
Every year the quality of applicants gets higher, which means that every year it becomes harder to get in. Applying with an obvious hole in your thought process is not going to help you stand out.