Depends on what kind of partner you’re looking for. If it’s more of a collaboration or long-term dev partner, places like Discord dev communities or GitHub discussion boards might be worth checking out to you.
There's also marketplaces like Upwork or similar platforms are more straightforward if you just want to hire someone, but community spaces tend to work better if you’re looking for someone to build with rather than just contract work.
On that note, you could post on here for that sort of thing, either on Joint Venture or Hire a Freelancer. Much luck.