Siri Suggestions are the most honest PMF test I know. Nobody asks you anything, it just watches what your thumb opens.
Mine: 3 AI agents, Maps, YouTube, WhatsApp, Uber and our own Neurable One.
If your product lands on your users' list, you have PMF.
ALT My iPhone Siri Suggestions: OpenBot, YouTube, Google Maps, Grok Bot, Neurable One, WhatsApp, Claude, Uber