Here's my advice:
- Location: while you can't search for a location, you can tell the YC platform your location, and set a radius, so that it only shows you profiles of people close to you.
- Meet people face to face: I had 20+ video calls and 10+ face-to-face meetings and I got SO MUCH more value from the face-to-face meetings. So much of finding a co-founder is about chemistry, and that's much easier to find/pick up on f2f.
- Do something different: Try to meet people for an activity, instead of just for a coffee. You'll get to know them in a much deeper sense.
- Explain who you're looking for clearly: don't feel like you need to appeal to everybody. I got a lot of success from making my profile very explicit "I'm looking for people who love XYZ and are motivated by ABC. I'm less interested in people that are looking for 123"
- Share your business idea: it may feel scary posting your idea to the world but if you have one, I suggest sharing your business idea clearly on your profile. It will attract people who want to work with you on it and repel people who have no interest in the space you want to work in.
- Persist: finding the right co-founder can take weeks/months/years. Expect to meet lots of the not-right people before you finally find the perfect match.
Hope that's helpful!