One tip I heard was asking “how” questions as follow-ups, rather than “what” questions? It tends to encourage people to think through how the conspiracies might actually work, rather than just jumping from point A to point B.

In my experience pure reasoning doesn't really work in that situation. People seek conspiracy theories to acquire a sense of order, predictability, and self worth. You're special because you're part of the special group that knows the true shape of the world. Ultimately, they seek love and validation, and the most effective intervention must start simply by providing them with those things they lack.

I followed closely a friend with schizophrenia and that helps me understand certain behaviors. Confronting them directly is usually pointless. I only wanted to be a good friend and show my care and affection for him. I did suggest him ways to improve but I backed away at any sign of resistance. You don't wanna counter him at every step, but only when they show an openness to listen. I mean, if you wanted to tear down a wall, you wouldn't start by hitting where it's stronger, right? You would probably look for the weak spots. If and when your friend let their guard down, then you can gently intervene. Other than that, just show them love, and have the patience to understand that they'll only change in their own time. If ever.